Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (9,021)	$ 11,724	$ (25,904)	$ 17,591
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on investments	26	(34)	94	(46)
Other comprehensive income (loss), net of tax	26	(34)	94	(46)
Comprehensive income (loss)	$ (8,995)	$ 11,690	$ (25,810)	$ 17,545