Consolidated statements of comprehensive income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 11,239	$ 15,775	$ 20,992	$ 30,374
Other comprehensive income, net of tax:
Net change in unrealized gain in available-for-sale securities, net of taxes of $1,053, $226, $1,408 and $764	1,631	3,564	2,180	11,770
Reclassification adjustment for gain on sale of securities included in net income, net of tax expense of $11, $84, $12 and $241	(18)	(2,507)	(18)	(3,750)
Comprehensive income	$ 12,852	$ 16,832	$ 23,154	$ 38,394