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, 2015		125	40,664,259
Beginning 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
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)
Comprehensive income
Net income	159,139				159,139
Other comprehensive income (loss), net of tax	(17,888)					(17,888)
Cash dividends on common stock	(41,660)				(41,660)
Reclassification adjustment under ASU 2018-02	0				626	(626)
Issuance of common stock related to acquisition
Share-based compensation (in shares)			112,569
Share-based compensation	3,592		$ 14	3,578
Stock Issued under employee benefit plans (in shares)			19,001
Stock issued under employee benefit plans	707		$ 2	705
Stock issued under dividend reinvestment and stock purchase plan (in shares)			28,156
Stock issued under dividend reinvestment and stock purchase plan	$ 1,211		$ 4	1,207
Stock options exercised (in shares)	76,152		76,152
Stock options exercised	$ 1,598		$ 10	1,588
Stock redeemed (in shares)			(44,316)
Stock redeemed	(1,902)		$ (6)	(1,896)
Ending balance (in shares) at Dec. 31, 2018		125	49,349,800
Ending balance at Dec. 31, 2018	$ 1,408,260	$ 125	$ 6,169	$ 840,052	$ 583,336	$ (21,422)