Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2015	Oct. 31, 2014	Oct. 31, 2015	Oct. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 29,461	$ 18,327	$ 71,412	$ 32,897
Other comprehensive income (loss):
Unrealized gains (losses) on investments	9	7	(15)	(14)
Other comprehensive income (loss), net of tax	9	7	(15)	(14)
Comprehensive income	$ 29,470	$ 18,334	$ 71,397	$ 32,883