Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 3,303	$ 8,632	$ 5,867	$ 10,415
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on investments	6	13	(12)	40
Other comprehensive income (loss), net of tax	6	13	(12)	40
Comprehensive income	$ 3,309	$ 8,645	$ 5,855	$ 10,455