Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (30,447)	$ 18,852	$ 57,810
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on investments	376	(209)	(63)
Other comprehensive income (loss), net of tax	376	(209)	(63)
Comprehensive income (loss)	$ (30,071)	$ 18,643	$ 57,747