Shareholder Report, Average Annual Return (Details)	12 Months Ended	60 Months Ended	120 Months Ended
Shareholder Report, Average Annual Return (Details)	Mar. 31, 2026	Mar. 31, 2026	Mar. 31, 2026
C000006083 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Class R Shares
Average Annual Return, Percent	22.92%	6.06%	10.26%
C000199765 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Class K Shares
Average Annual Return, Percent	23.53%	6.63%	10.86%
C000006081 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Investor C Shares (with sales charge)
Average Annual Return, Percent	21.30%	5.52%	9.87%
C000006079 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Investor A Shares (with sales charge)
Average Annual Return, Percent	16.71%	5.17%	9.95%
C000006082 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Institutional Shares
Average Annual Return, Percent	23.48%	6.58%	10.82%
Without Sales Load [Member] \| C000006081 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Investor C Shares
Average Annual Return, Percent	22.30%	5.52%	9.87%
Without Sales Load [Member] \| C000006079 [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Investor A Shares
Average Annual Return, Percent	23.18%	6.32%	10.54%
Russell 3000 Index [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Russell 3000® Index
Average Annual Return, Percent	18.09%	10.87%	13.72%
Russell 2500 Index [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Russell 2500® Index
Average Annual Return, Percent	23.45%	5.48%	10.58%