Income Taxes - Reconciliation of income tax computed at the federal statutory rate to the company's effective income tax rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2014
Income Tax Disclosure [Abstract]
Goodwill, time period deductible for Income tax	15 years
Tax at U.S. federal statutory rate	35.00%	35.00%	35.00%
State and local income taxes, net of U.S. federal benefit	2.10%	(0.30%)	1.50%
Tax credit for research activities	(8.80%)	(3.90%)	(1.20%)
Effective income tax rate reconciliation, Tax benefit from insurance premium	(3.90%)	(1.00%)	0.00%
Tax benefit on qualified production activities	(3.80%)	(3.60%)	(2.90%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent	0.00%	0.70%	0.20%
Effective income tax rate	20.60%	26.90%	32.60%
Favorable prior year tax benefit		$ 776
Discrete tax benefit		$ 963