Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 76,508	$ 50,571	$ 25,654
Other comprehensive loss:
Unrealized losses on investments	(6)	(1)	0
Other comprehensive loss, net of tax	(6)	(1)	0
Comprehensive income	$ 76,502	$ 50,570	$ 25,654