Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income		$ 16,956	$ 15,481	$ 33,125	$ 29,005
Other comprehensive income:
Unrealized gain (loss) on securities, net of tax	[1]	153	1,956	(5,695)	2,908
Comprehensive income		$ 17,109	$ 17,437	$ 27,430	$ 31,913

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