INCOME TAXES - Reconciliation of Expected Income Tax Expense to Actual Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017	Jan. 31, 2018
Computed expected income tax expense			$ 6,266	$ 25,810
State income taxes, net of federal tax benefit			1,176	3,020
Domestic production activities deduction				(2,148)
Stock options			(5)	(773)
Adjustments and other differences			614	(233)
Income tax expense	$ 6,314	$ 14,601	8,051	25,676
Prepaid income taxes	$ 3,200		3,200		$ 7,900
Research and development
Income tax expense			$ 0	$ 0	$ 0