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, 2017		125	49,158,238
Beginning balance at Dec. 31, 2017	$ 1,303,463	$ 125	$ 6,145	$ 834,870	$ 465,231	$ (2,908)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
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)
Percent of outstanding shares	0
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
Stock options exercised	1,598		$ 10	1,588
Restricted shares withheld for taxes (in shares)			(44,316)
Restricted shares withheld for taxes	(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)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income	164,460				164,460
Other comprehensive income (loss), net of tax	49,296					49,296
Cash dividends on common stock	(51,276)				(51,276)
Issuance of common stock related to acquisitions (in shares)			6,383,806
Percent of outstanding shares	229,926		$ 798	229,128
Repurchases of common stock (in shares)			(516,016)
Repurchases of common stock	(19,041)		$ (65)	(18,976)
Share-based compensation (in shares)			116,572
Share-based compensation	4,115		$ 15	4,100
Stock issued under employee benefit plans (in shares)			21,521
Stock issued under employee benefit plans	702		$ 3	699
Stock issued under dividend reinvestment and stock purchase plan (in shares)			38,942
Stock issued under dividend reinvestment and stock purchase plan	1,531		$ 5	1,526
Stock options exercised (in shares)			16,950
Stock options exercised	144		$ 2	142
Restricted shares withheld for taxes (in shares)			(43,093)
Restricted shares withheld for taxes	(1,680)		$ (6)	(1,674)
Ending balance (in shares) at Dec. 31, 2019		125	55,368,482
Ending balance at Dec. 31, 2019	1,786,437	$ 125	$ 6,921	1,054,997	696,520	27,874
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income	148,600				148,600
Other comprehensive income (loss), net of tax	46,962					46,962
Cash dividends on common stock	(56,542)				(56,542)
Percent of outstanding shares	0
Repurchases of common stock (in shares)			(1,634,437)
Repurchases of common stock	(55,912)		$ (204)	(55,708)
Share-based compensation (in shares)			128,292
Share-based compensation	4,600		$ 16	4,584
Stock issued under employee benefit plans (in shares)			25,423
Stock issued under employee benefit plans	639		$ 3	636
Stock issued under dividend reinvestment and stock purchase plan (in shares)			60,806
Stock issued under dividend reinvestment and stock purchase plan	$ 1,726		$ 8	1,718
Stock options exercised (in shares)	13,550		13,550
Stock options exercised	$ 115		$ 2	113
Restricted shares withheld for taxes (in shares)			(39,757)
Restricted shares withheld for taxes	(980)		$ (6)	(974)
Ending balance (in shares) at Dec. 31, 2020		125	53,922,359
Ending balance at Dec. 31, 2020	$ 1,875,645	$ 125	$ 6,740	$ 1,005,366	$ 788,578	$ 74,836