Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income		$ 19,701	$ 16,577	$ 52,826	$ 45,582
Other comprehensive income:
Unrealized gain (loss) on securities, net of tax	[1]	(2,118)	617	(7,813)	3,525
Comprehensive income		$ 17,583	$ 17,194	$ 45,013	$ 49,107

[1] Data presented for 2018 includes debt securities only compared to 2017 which includes both debt and equity securities.