INCOME TAXES - Income Tax Expense Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
INCOME TAXES
Computed expected income tax expense	$ (9,916)	$ (38,078)	$ (40,086)
Federal research and development tax credits	13,866
State income taxes, net of federal tax effect	683	(5,042)	(4,001)
Net operating loss carryforwards	1,730
Stock options	32	962	4,969
Domestic production activities deduction		3,204	2,906
Other permanent differences, net	(1,585)	(1,141)	551
Impact of the federal tax rate change on deferred taxes		789
Adjustments and other differences	(159)	(973)	(1,445)
Income tax benefit (expense)	4,651	(40,279)	$ (37,106)
Research and development state tax credit	2,800
Income tax refunds and prepaid income taxes	19,500
Prepaid income taxes		$ 7,900
Income tax benefit recorded related to additional net operating losses of acquired companies	$ 1,700