Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 16,577	$ 17,896	$ 45,582	$ 58,792
Other comprehensive income:
Unrealized gain (loss) on securities, net of tax	617	(1,713)	3,525	4,009
Comprehensive income	$ 17,194	$ 16,183	$ 49,107	$ 62,801