Income Taxes - Actual Income Tax Expense Amounts (Detail) (USD $)	12 Months Ended
	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2012
Income Tax Disclosure [Abstract]
Computed "expected" income tax	$ 24,267,000	$ 12,510,000	$ 4,068,000
Increase (decrease) resulting from:
State income taxes, net	2,574,000	1,459,000	460,000
Permanent differences	(1,105,000)	(730,000)	(138,000)
Federal income tax true-up and other adjustments	255,000	401,000	166,000
Income tax expense	$ 25,991,000	$ 13,640,000	$ 4,556,000