Income Taxes Reconciliation of income tax computed at the federal statutory rate to the company's effective income tax rate (Details)	12 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2010
Income Tax Disclosure [Abstract]
Tax at U.S. federal statutory rate	35.00%	35.00%	35.00%
State and local income taxes, net of U.S. federal benefit	1.00%	1.30%	1.30%
Tax benefit on qualified production activities	(2.40%)	(3.00%)	(2.10%)
Tax credit for research activities	(0.70%)	(0.70%)	(0.70%)
Other, net	0.20%	0.20%	0.50%
Effective income tax rate	33.10%	32.80%	34.00%