v3.26.3
Shareholder Report, Holdings (Details)
Jun. 30, 2026
Needham Growth Fund | Institutional Class | Information Technology  
Holdings [Line Items]  
Percent of Net Asset Value 52.10%
Needham Growth Fund | Institutional Class | Industrials  
Holdings [Line Items]  
Percent of Net Asset Value 24.60%
Needham Growth Fund | Institutional Class | Health Care [Member]  
Holdings [Line Items]  
Percent of Net Asset Value 5.80%
Needham Growth Fund | Institutional Class | Communication Services  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Needham Growth Fund | Institutional Class | Consumer Discretionary  
Holdings [Line Items]  
Percent of Net Asset Value 1.40%
Needham Growth Fund | Institutional Class | Financials  
Holdings [Line Items]  
Percent of Net Asset Value 1.10%
Needham Growth Fund | Institutional Class | Materials  
Holdings [Line Items]  
Percent of Net Asset Value 1.10%
Needham Growth Fund | Institutional Class | Real Estate [Member]  
Holdings [Line Items]  
Percent of Net Asset Value 0.70%
Needham Growth Fund | Institutional Class | Energy  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Needham Growth Fund | Institutional Class | Cash & Other  
Holdings [Line Items]  
Percent of Net Asset Value 10.50%
Needham Growth Fund | Institutional Class | Dreyfus Treasury Securities Cash Management  
Holdings [Line Items]  
Percent of Net Asset Value 10.30%
Needham Growth Fund | Institutional Class | PDF Solutions, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 5.30%
Needham Growth Fund | Institutional Class | Corning, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 3.70%
Needham Growth Fund | Institutional Class | Lam Research Corp.  
Holdings [Line Items]  
Percent of Net Asset Value 3.70%
Needham Growth Fund | Institutional Class | Vicor Corp.  
Holdings [Line Items]  
Percent of Net Asset Value 3.50%
Needham Growth Fund | Institutional Class | Vishay Intertechnology, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 3.50%
Needham Growth Fund | Institutional Class | FormFactor, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
Needham Growth Fund | Institutional Class | Marvell Technology, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 3.10%
Needham Growth Fund | Institutional Class | MKS, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 3.00%
Needham Growth Fund | Institutional Class | Vertiv Holdings Co.  
Holdings [Line Items]  
Percent of Net Asset Value 2.90%
Needham Growth Fund | Retail Class | Information Technology  
Holdings [Line Items]  
Percent of Net Asset Value 52.10%
Needham Growth Fund | Retail Class | Industrials  
Holdings [Line Items]  
Percent of Net Asset Value 24.60%
Needham Growth Fund | Retail Class | Health Care [Member]  
Holdings [Line Items]  
Percent of Net Asset Value 5.80%
Needham Growth Fund | Retail Class | Communication Services  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Needham Growth Fund | Retail Class | Consumer Discretionary  
Holdings [Line Items]  
Percent of Net Asset Value 1.40%
Needham Growth Fund | Retail Class | Financials  
Holdings [Line Items]  
Percent of Net Asset Value 1.10%
Needham Growth Fund | Retail Class | Materials  
Holdings [Line Items]  
Percent of Net Asset Value 1.10%
Needham Growth Fund | Retail Class | Real Estate [Member]  
Holdings [Line Items]  
Percent of Net Asset Value 0.70%
Needham Growth Fund | Retail Class | Energy  
Holdings [Line Items]  
Percent of Net Asset Value 0.30%
Needham Growth Fund | Retail Class | Cash & Other  
Holdings [Line Items]  
Percent of Net Asset Value 10.50%
Needham Growth Fund | Retail Class | Dreyfus Treasury Securities Cash Management  
Holdings [Line Items]  
Percent of Net Asset Value 10.30%
Needham Growth Fund | Retail Class | PDF Solutions, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 5.30%
Needham Growth Fund | Retail Class | Corning, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 3.70%
Needham Growth Fund | Retail Class | Lam Research Corp.  
Holdings [Line Items]  
Percent of Net Asset Value 3.70%
Needham Growth Fund | Retail Class | Vicor Corp.  
Holdings [Line Items]  
Percent of Net Asset Value 3.50%
Needham Growth Fund | Retail Class | Vishay Intertechnology, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 3.50%
Needham Growth Fund | Retail Class | FormFactor, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 3.40%
Needham Growth Fund | Retail Class | Marvell Technology, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 3.10%
Needham Growth Fund | Retail Class | MKS, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 3.00%
Needham Growth Fund | Retail Class | Vertiv Holdings Co.  
Holdings [Line Items]  
Percent of Net Asset Value 2.90%
Needham Aggressive Growth Fund | Institutional Class | Information Technology  
Holdings [Line Items]  
Percent of Net Asset Value 40.60%
Needham Aggressive Growth Fund | Institutional Class | Industrials  
Holdings [Line Items]  
Percent of Net Asset Value 32.90%
Needham Aggressive Growth Fund | Institutional Class | Health Care [Member]  
Holdings [Line Items]  
Percent of Net Asset Value 1.60%
Needham Aggressive Growth Fund | Institutional Class | Communication Services  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Needham Aggressive Growth Fund | Institutional Class | Consumer Discretionary  
Holdings [Line Items]  
Percent of Net Asset Value 9.00%
Needham Aggressive Growth Fund | Institutional Class | Materials  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Needham Aggressive Growth Fund | Institutional Class | Real Estate [Member]  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Needham Aggressive Growth Fund | Institutional Class | Energy  
Holdings [Line Items]  
Percent of Net Asset Value 4.10%
Needham Aggressive Growth Fund | Institutional Class | Cash & Other  
Holdings [Line Items]  
Percent of Net Asset Value 5.30%
Needham Aggressive Growth Fund | Institutional Class | Consumer Staples  
Holdings [Line Items]  
Percent of Net Asset Value 3.20%
Needham Aggressive Growth Fund | Institutional Class | Dreyfus Treasury Securities Cash Management  
Holdings [Line Items]  
Percent of Net Asset Value 4.60%
Needham Aggressive Growth Fund | Institutional Class | PDF Solutions, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 4.60%
Needham Aggressive Growth Fund | Institutional Class | Vicor Corp.  
Holdings [Line Items]  
Percent of Net Asset Value 6.90%
Needham Aggressive Growth Fund | Institutional Class | Vishay Intertechnology, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Needham Aggressive Growth Fund | Institutional Class | Vertiv Holdings Co.  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Needham Aggressive Growth Fund | Institutional Class | Arteris, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 5.90%
Needham Aggressive Growth Fund | Institutional Class | nLight, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 4.50%
Needham Aggressive Growth Fund | Institutional Class | Vishay Precision Group, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Needham Aggressive Growth Fund | Institutional Class | CECO Environmental Corp.  
Holdings [Line Items]  
Percent of Net Asset Value 3.20%
Needham Aggressive Growth Fund | Institutional Class | Oil-Dri Corp. of America  
Holdings [Line Items]  
Percent of Net Asset Value 2.70%
Needham Aggressive Growth Fund | Retail Class | Information Technology  
Holdings [Line Items]  
Percent of Net Asset Value 40.60%
Needham Aggressive Growth Fund | Retail Class | Industrials  
Holdings [Line Items]  
Percent of Net Asset Value 32.90%
Needham Aggressive Growth Fund | Retail Class | Health Care [Member]  
Holdings [Line Items]  
Percent of Net Asset Value 1.60%
Needham Aggressive Growth Fund | Retail Class | Communication Services  
Holdings [Line Items]  
Percent of Net Asset Value 0.40%
Needham Aggressive Growth Fund | Retail Class | Consumer Discretionary  
Holdings [Line Items]  
Percent of Net Asset Value 9.00%
Needham Aggressive Growth Fund | Retail Class | Materials  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Needham Aggressive Growth Fund | Retail Class | Real Estate [Member]  
Holdings [Line Items]  
Percent of Net Asset Value 0.50%
Needham Aggressive Growth Fund | Retail Class | Energy  
Holdings [Line Items]  
Percent of Net Asset Value 4.10%
Needham Aggressive Growth Fund | Retail Class | Cash & Other  
Holdings [Line Items]  
Percent of Net Asset Value 5.30%
Needham Aggressive Growth Fund | Retail Class | Consumer Staples  
Holdings [Line Items]  
Percent of Net Asset Value 3.20%
Needham Aggressive Growth Fund | Retail Class | Dreyfus Treasury Securities Cash Management  
Holdings [Line Items]  
Percent of Net Asset Value 4.60%
Needham Aggressive Growth Fund | Retail Class | PDF Solutions, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 4.60%
Needham Aggressive Growth Fund | Retail Class | Vicor Corp.  
Holdings [Line Items]  
Percent of Net Asset Value 6.90%
Needham Aggressive Growth Fund | Retail Class | Vishay Intertechnology, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 4.80%
Needham Aggressive Growth Fund | Retail Class | Vertiv Holdings Co.  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Needham Aggressive Growth Fund | Retail Class | Arteris, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 5.90%
Needham Aggressive Growth Fund | Retail Class | nLight, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 4.50%
Needham Aggressive Growth Fund | Retail Class | Vishay Precision Group, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 3.30%
Needham Aggressive Growth Fund | Retail Class | CECO Environmental Corp.  
Holdings [Line Items]  
Percent of Net Asset Value 3.20%
Needham Aggressive Growth Fund | Retail Class | Oil-Dri Corp. of America  
Holdings [Line Items]  
Percent of Net Asset Value 2.70%
Needham Small Cap Growth Fund | Institutional Class | Information Technology  
Holdings [Line Items]  
Percent of Net Asset Value 59.40%
Needham Small Cap Growth Fund | Institutional Class | Industrials  
Holdings [Line Items]  
Percent of Net Asset Value 16.60%
Needham Small Cap Growth Fund | Institutional Class | Health Care [Member]  
Holdings [Line Items]  
Percent of Net Asset Value 2.70%
Needham Small Cap Growth Fund | Institutional Class | Consumer Discretionary  
Holdings [Line Items]  
Percent of Net Asset Value 4.40%
Needham Small Cap Growth Fund | Institutional Class | Materials  
Holdings [Line Items]  
Percent of Net Asset Value 1.90%
Needham Small Cap Growth Fund | Institutional Class | Real Estate [Member]  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Needham Small Cap Growth Fund | Institutional Class | Energy  
Holdings [Line Items]  
Percent of Net Asset Value 1.50%
Needham Small Cap Growth Fund | Institutional Class | Cash & Other  
Holdings [Line Items]  
Percent of Net Asset Value 12.50%
Needham Small Cap Growth Fund | Institutional Class | Utilities  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
Needham Small Cap Growth Fund | Institutional Class | Dreyfus Treasury Securities Cash Management  
Holdings [Line Items]  
Percent of Net Asset Value 14.30%
Needham Small Cap Growth Fund | Institutional Class | PDF Solutions, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Needham Small Cap Growth Fund | Institutional Class | Vishay Intertechnology, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 5.00%
Needham Small Cap Growth Fund | Institutional Class | Arteris, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 8.70%
Needham Small Cap Growth Fund | Institutional Class | Badger Meter, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 5.10%
Needham Small Cap Growth Fund | Institutional Class | Ambarella, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 2.80%
Needham Small Cap Growth Fund | Institutional Class | Harmonic, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 2.70%
Needham Small Cap Growth Fund | Institutional Class | Veeco Instruments, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 2.60%
Needham Small Cap Growth Fund | Institutional Class | Calix, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Needham Small Cap Growth Fund | Institutional Class | CEVA, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Needham Small Cap Growth Fund | Retail Class | Information Technology  
Holdings [Line Items]  
Percent of Net Asset Value 59.40%
Needham Small Cap Growth Fund | Retail Class | Industrials  
Holdings [Line Items]  
Percent of Net Asset Value 16.60%
Needham Small Cap Growth Fund | Retail Class | Health Care [Member]  
Holdings [Line Items]  
Percent of Net Asset Value 2.70%
Needham Small Cap Growth Fund | Retail Class | Consumer Discretionary  
Holdings [Line Items]  
Percent of Net Asset Value 4.40%
Needham Small Cap Growth Fund | Retail Class | Materials  
Holdings [Line Items]  
Percent of Net Asset Value 1.90%
Needham Small Cap Growth Fund | Retail Class | Real Estate [Member]  
Holdings [Line Items]  
Percent of Net Asset Value 0.20%
Needham Small Cap Growth Fund | Retail Class | Energy  
Holdings [Line Items]  
Percent of Net Asset Value 1.50%
Needham Small Cap Growth Fund | Retail Class | Cash & Other  
Holdings [Line Items]  
Percent of Net Asset Value 12.50%
Needham Small Cap Growth Fund | Retail Class | Utilities  
Holdings [Line Items]  
Percent of Net Asset Value 0.80%
Needham Small Cap Growth Fund | Retail Class | Dreyfus Treasury Securities Cash Management  
Holdings [Line Items]  
Percent of Net Asset Value 14.30%
Needham Small Cap Growth Fund | Retail Class | PDF Solutions, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Needham Small Cap Growth Fund | Retail Class | Vishay Intertechnology, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 5.00%
Needham Small Cap Growth Fund | Retail Class | Arteris, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 8.70%
Needham Small Cap Growth Fund | Retail Class | Badger Meter, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 5.10%
Needham Small Cap Growth Fund | Retail Class | Ambarella, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 2.80%
Needham Small Cap Growth Fund | Retail Class | Harmonic, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 2.70%
Needham Small Cap Growth Fund | Retail Class | Veeco Instruments, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 2.60%
Needham Small Cap Growth Fund | Retail Class | Calix, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%
Needham Small Cap Growth Fund | Retail Class | CEVA, Inc.  
Holdings [Line Items]  
Percent of Net Asset Value 2.40%