CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Preferred	Common Stock	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2014		125	37,669,948
Beginning balance at Dec. 31, 2014	$ 726,827	$ 125	$ 4,709	$ 431,220	$ 292,403	$ (1,630)
Comprehensive income
Net income	65,384				65,384
Other comprehensive income (loss), net of tax	268					268
Cash dividends on common stock	(15,654)				(15,654)
Issuance of common stock related to acquisition (in shares)			2,769,568
Issuance of common stock related to acquisition	70,402		$ 346	70,056
Share-based compensation (in shares)			149,577
Share-based compensation	2,270		$ 19	2,251
Stock Issued under employee benefit plans (in shares)			22,074
Stock issued under employee benefit plans	460		$ 3	457
Stock issued under dividend reinvestment and stock purchase plan (in shares)			26,375
Stock issued under dividend reinvestment and stock purchase plan	661		$ 3	658
Stock options exercised (in shares)			96,066
Stock options exercised	1,531		$ 12	1,519
Stock redeemed (in shares)			(69,349)
Stock redeemed	(1,640)		$ (9)	(1,631)
Ending balance (in shares) at Dec. 31, 2015		125	40,664,259
Ending balance at Dec. 31, 2015	850,509	$ 125	$ 5,083	504,530	342,133	(1,362)
Comprehensive income
Net income	81,051				81,051
Other comprehensive income (loss), net of tax	(12,219)					(12,219)
Cash dividends on common stock	(22,203)				(22,203)
Issuance of common stock related to acquisition
Share-based compensation (in shares)			141,126
Share-based compensation	2,600		$ 17	2,583
Stock Issued under employee benefit plans (in shares)			20,545
Stock issued under employee benefit plans	462		$ 3	459
Stock issued under dividend reinvestment and stock purchase plan (in shares)			30,297
Stock issued under dividend reinvestment and stock purchase plan	835		$ 4	831
Stock options exercised (in shares)			128,848
Stock options exercised	2,602		$ 16	2,586
Stock redeemed (in shares)			(72,378)
Stock redeemed	(1,980)		$ (9)	(1,971)
Ending balance (in shares) at Dec. 31, 2016		125	40,912,697
Ending balance at Dec. 31, 2016	901,657	$ 125	$ 5,114	509,018	400,981	(13,581)
Comprehensive income
Net income	96,070				96,070
Other comprehensive income (loss), net of tax	10,673					10,673
Cash dividends on common stock	(31,820)				(31,820)
Issuance of common stock related to acquisition (in shares)			8,044,446
Issuance of common stock related to acquisition	321,431		$ 1,006	320,425
Share-based compensation (in shares)			89,362
Share-based compensation	2,827		$ 11	2,816
Stock Issued under employee benefit plans (in shares)			14,948
Stock issued under employee benefit plans	519		$ 2	517
Stock issued under dividend reinvestment and stock purchase plan (in shares)			24,058
Stock issued under dividend reinvestment and stock purchase plan	$ 991		$ 3	988
Stock options exercised (in shares)	104,748		104,748
Stock options exercised	$ 2,398		$ 13	2,385
Stock redeemed (in shares)			(32,021)
Stock redeemed	(1,283)		$ (4)	(1,279)
Ending balance (in shares) at Dec. 31, 2017		125	49,158,238
Ending balance at Dec. 31, 2017	$ 1,303,463	$ 125	$ 6,145	$ 834,870	$ 465,231	$ (2,908)