Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2016	Jul. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 8,632	$ 23,097	$ 10,415	$ 41,951
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on investments	13	(7)	40	(23)
Other comprehensive income (loss), net of tax	13	(7)	40	(23)
Comprehensive income	$ 8,645	$ 23,090	$ 10,455	$ 41,928