Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 57,810	$ 76,508	$ 50,571
Other comprehensive loss, net of tax:
Unrealized losses on investments	(63)	(6)	(1)
Other comprehensive loss, net of tax	(63)	(6)	(1)
Comprehensive income	$ 57,747	$ 76,502	$ 50,570