Income Taxes - Components of Company's Income Tax Expense Related to Continuing Operations (Detail) (USD $)	12 Months Ended
	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2012
Current:
Federal	$ 20,765,000	$ 11,555,000	$ 3,771,000
State	3,525,000	2,224,000	836,000
Total	24,290,000	13,779,000	4,607,000
Deferred:
Federal	1,419,000	(207,000)	41,000
State	282,000	68,000	(92,000)
Total	1,701,000	(139,000)	(51,000)
Income tax expense	$ 25,991,000	$ 13,640,000	$ 4,556,000