INCOME TAXES - Components of Company's Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Current:
Federal	$ 29,681	$ 16,458	$ 15,249
State	6,188	5,423	4,767
Total	35,869	21,881	20,016
Deferred:
Federal	1,277	2,950	788
State	(40)	471	108
Total	1,237	3,421	896
Income tax expense	$ 37,106	$ 25,302	$ 20,912