Shareholder Report, Average Annual Return (Details)
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12 Months Ended |
60 Months Ended |
93 Months Ended |
108 Months Ended |
120 Months Ended |
Jul. 31, 2025 |
Jul. 31, 2025 |
Jul. 31, 2025 |
Jul. 31, 2025 |
Jul. 31, 2025 |
| Kansas Municipal Fund | Class A [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
KSMUX with maximum sales charge
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| Average Annual Return, Percent |
(4.69%)
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(2.09%)
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0.51%
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| Kansas Municipal Fund | Class I [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
KSITX
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| Average Annual Return, Percent |
(1.98%)
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(1.32%)
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0.59%
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[1] |
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| Maine Municipal Fund | Class A [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
MEMUX with maximum sales charge
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| Average Annual Return, Percent |
(4.31%)
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(2.03%)
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0.09%
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| Maine Municipal Fund | Class I [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
MEIMX
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| Average Annual Return, Percent |
(1.55%)
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(1.29%)
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0.19%
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[2] |
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| Nebraska Municipal Fund | Class A [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
NEMUX with maximum sales charge
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| Average Annual Return, Percent |
(4.85%)
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(2.17%)
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0.34%
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| Nebraska Municipal Fund | Class I [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
NEITX
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| Average Annual Return, Percent |
(2.07%)
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(1.40%)
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0.38%
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[3] |
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| Oklahoma Municipal Fund | Class A [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
OKMUX with maximum sales charge
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| Average Annual Return, Percent |
(3.53%)
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(1.75%)
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0.63%
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| Oklahoma Municipal Fund | Class I [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
OKMIX
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| Average Annual Return, Percent |
(0.92%)
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(1.02%)
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0.66%
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[4] |
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| Viking Tax-Free Fund for Montana | Class A [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
VMTTX with maximum sales charge
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| Average Annual Return, Percent |
(3.59%)
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(1.52%)
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0.66%
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| Viking Tax-Free Fund for Montana | Class I [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
VMTIX
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| Average Annual Return, Percent |
(0.92%)
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(0.76%)
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0.69%
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[5] |
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| Viking Tax-Free Fund for North Dakota | Class A [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
VNDFX with maximum sales charge
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| Average Annual Return, Percent |
(5.23%)
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(2.30%)
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0.11%
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| Viking Tax-Free Fund for North Dakota | Class I [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
VNDIX
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| Average Annual Return, Percent |
(2.57%)
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(1.55%)
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0.07%
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[6] |
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| Without Sales Load [Member] | Kansas Municipal Fund | Class A [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
KSMUX without maximum sales charge
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| Average Annual Return, Percent |
(2.23%)
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(1.58%)
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0.76%
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| Without Sales Load [Member] | Maine Municipal Fund | Class A [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
MEMUX without maximum sales charge
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| Average Annual Return, Percent |
(1.90%)
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(1.53%)
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0.34%
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| Without Sales Load [Member] | Nebraska Municipal Fund | Class A [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
NEMUX without maximum sales charge
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| Average Annual Return, Percent |
(2.41%)
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(1.66%)
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0.59%
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| Without Sales Load [Member] | Oklahoma Municipal Fund | Class A [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
OKMUX without maximum sales charge
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| Average Annual Return, Percent |
(1.07%)
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(1.26%)
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0.89%
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| Without Sales Load [Member] | Viking Tax-Free Fund for Montana | Class A [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
VMTTX without maximum sales Charge
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| Average Annual Return, Percent |
(1.16%)
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(1.01%)
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0.92%
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| Without Sales Load [Member] | Viking Tax-Free Fund for North Dakota | Class A [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
VNDFX without maximum sales charge
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| Average Annual Return, Percent |
(2.81%)
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(1.80%)
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0.36%
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| Kansas Municipal Fund | Class A | Bloomberg U.S. Municipal Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
Bloomberg U.S. Municipal Bond Index
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| Kansas Municipal Fund | Class A | Bloomberg U.S. Muni Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Average Annual Return, Percent |
0.00%
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0.13%
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2.11%
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| Kansas Municipal Fund | Class I | Bloomberg U.S. Municipal Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
Bloomberg U.S. Municipal Bond Index
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| Kansas Municipal Fund | Class I | Bloomberg U.S. Muni Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Average Annual Return, Percent |
0.00%
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0.13%
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1.75%
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[1] |
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| Maine Municipal Fund | Class A | Bloomberg U.S. Municipal Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
Bloomberg U.S. Municipal Bond Index
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| Maine Municipal Fund | Class A | Bloomberg U.S. Muni Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Average Annual Return, Percent |
0.00%
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0.13%
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2.11%
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| Maine Municipal Fund | Class I | Bloomberg U.S. Municipal Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
Bloomberg U.S. Municipal Bond Index
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| Maine Municipal Fund | Class I | Bloomberg U.S. Muni Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Average Annual Return, Percent |
0.00%
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0.13%
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1.75%
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[2] |
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| Nebraska Municipal Fund | Class A | Bloomberg U.S. Municipal Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
Bloomberg U.S. Municipal Bond Index
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| Nebraska Municipal Fund | Class A | Bloomberg U.S. Muni Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Average Annual Return, Percent |
0.00%
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0.13%
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2.11%
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| Nebraska Municipal Fund | Class I | Bloomberg U.S. Municipal Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
Bloomberg U.S. Municipal Bond Index
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| Nebraska Municipal Fund | Class I | Bloomberg U.S. Muni Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Average Annual Return, Percent |
0.00%
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0.13%
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1.75%
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[3] |
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| Oklahoma Municipal Fund | Class A | Bloomberg U.S. Municipal Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
Bloomberg U.S. Municipal Bond Index
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| Oklahoma Municipal Fund | Class A | Bloomberg U.S. Muni Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Average Annual Return, Percent |
0.00%
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0.13%
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2.11%
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| Oklahoma Municipal Fund | Class I | Bloomberg U.S. Municipal Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
Bloomberg U.S. Municipal Bond Index
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| Oklahoma Municipal Fund | Class I | Bloomberg U.S. Muni Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Average Annual Return, Percent |
0.00%
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0.13%
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1.75%
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[4] |
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| Viking Tax-Free Fund for Montana | Class A | Bloomberg U.S. Municipal Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
Bloomberg U.S. Municipal Bond Index
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| Viking Tax-Free Fund for Montana | Class A | Bloomberg U.S. Muni Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Average Annual Return, Percent |
0.00%
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0.13%
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2.11%
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| Viking Tax-Free Fund for Montana | Class I | Bloomberg U.S. Municipal Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
Bloomberg U.S. Municipal Bond Index
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| Viking Tax-Free Fund for Montana | Class I | Bloomberg U.S. Muni Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Average Annual Return, Percent |
0.00%
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0.13%
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1.59%
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[5] |
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| Viking Tax-Free Fund for North Dakota | Class A | Bloomberg U.S. Municipal Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
Bloomberg U.S. Municipal Bond Index
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| Viking Tax-Free Fund for North Dakota | Class A | Bloomberg U.S. Muni Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Average Annual Return, Percent |
0.00%
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0.13%
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2.11%
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| Viking Tax-Free Fund for North Dakota | Class I | Bloomberg U.S. Municipal Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Line Graph and Table Measure Name |
Bloomberg U.S. Municipal Bond Index
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| Viking Tax-Free Fund for North Dakota | Class I | Bloomberg U.S. Muni Bond Index [Member] |
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| Average Annual Return [Line Items] |
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| Average Annual Return, Percent |
0.00%
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0.13%
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1.59%
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[6] |
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