Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative adjustment for adoption of ASU 2016-01				$ 0
Adjusted equity balance				593
Balance at beginning of period at Dec. 31, 2016	$ 550,044	$ 510,861	$ 38,590	593
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	12,312		12,312
Other comprehensive loss, net of tax	(901)			(901)
Stock based compensation	1,170	1,170
Exercise of stock options	300	300
Retirement of restricted stock	(756)	(756)
Cash dividends, common stock	(4,527)		(4,527)
Balance at end of period at Mar. 31, 2017	557,642	511,575	46,375	(308)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative adjustment for adoption of ASU 2016-01	0	0	2,043	(2,043)
Adjusted equity balance	583,122	512,734	74,780	(4,392)
Balance at beginning of period at Dec. 31, 2017	583,122	512,734	72,737	(2,349)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	15,255		15,255
Other comprehensive loss, net of tax	(5,449)			(5,449)
Stock based compensation	994	994
Exercise of stock options	248	248
Retirement of restricted stock	(744)	(744)
Cash dividends, common stock	(4,778)		(4,778)
Balance at end of period at Mar. 31, 2018	$ 588,648	$ 513,232	$ 85,257	$ (9,841)