Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Adoption of new accounting standard	Preferred Stock	Common Stock	Common Stock Issuable	Capital Surplus	Retained Earnings (Accumulated Deficit)	Retained Earnings (Accumulated Deficit) Adoption of new accounting standard	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2018	$ 1,457,554	$ (549)	$ 0	$ 79,234	$ 10,744	$ 1,499,584	$ (90,419)	$ (549)	$ (41,589)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	136,709						136,709
Other comprehensive income	55,852								55,852
Exercise of stock options	197			12		185
Common stock issued to dividend reinvestment plan and employee benefit plans	2,004			76		1,928
Common stock issued for acquisition	0
Amortization of restricted stock unit awards	7,680					7,680
Vesting of restricted stock unit awards, net of shares surrendered to cover payroll taxes	(1,022)			81	1,365	(2,468)
Purchases of common stock	(13,020)			(500)		(12,520)
Deferred compensation plan, net, including dividend equivalents	406				406
Common stock issued from deferred compensation plan, net of shares surrendered to cover payroll taxes	(239)			71	(1,188)	878
Common stock dividends	(40,147)						(40,147)
Ending balance at Sep. 30, 2019	1,605,425		0	78,974	11,327	1,495,267	5,594		14,263
Beginning balance at Jun. 30, 2019	1,566,334		0	79,075	10,858	1,498,740	(29,116)		6,777
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	48,362						48,362
Other comprehensive income	7,486								7,486
Exercise of stock options	0
Common stock issued to dividend reinvestment plan and employee benefit plans	913			34		879
Amortization of restricted stock unit awards	1,678					1,678
Vesting of restricted stock unit awards, net of shares surrendered to cover payroll taxes	(630)			60	356	(1,046)
Purchases of common stock	(5,180)			(195)		(4,985)
Deferred compensation plan, net, including dividend equivalents	114				114
Common stock issued from deferred compensation plan, net of shares surrendered to cover payroll taxes	0				(1)	1
Common stock dividends	(13,652)						(13,652)
Ending balance at Sep. 30, 2019	1,605,425		0	78,974	11,327	1,495,267	5,594		14,263
Beginning balance at Dec. 31, 2019	1,635,692	$ (3,529)	0	79,014	11,491	1,496,641	40,152	$ (3,529)	8,394
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	104,587						104,587
Other comprehensive income	32,791								32,791
Issuance of stock	96,422		96,422
Common stock issued to dividend reinvestment plan and employee benefit plans	1,078			60		1,018
Common stock issued for acquisition	163,589			8,131		155,458
Amortization of restricted stock unit awards	5,939					5,939
Vesting of restricted stock unit awards, net of shares surrendered to cover payroll taxes	(1,322)			151	1,008	(2,481)
Purchases of common stock	(20,782)			(827)		(19,955)
Deferred compensation plan, net, including dividend equivalents	380				380
Common stock issued from deferred compensation plan, net of shares surrendered to cover payroll taxes	(1,318)			82	(2,247)	847
Preferred stock dividends	(1,814)						(1,814)
Common stock dividends	(44,458)						(44,458)
Ending balance at Sep. 30, 2020	1,967,255		96,422	86,611	10,632	1,637,467	94,938		41,185
Beginning balance at Jun. 30, 2020	1,771,645		96,660	78,335	10,646	1,480,464	64,990		40,550
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	47,607						47,607
Other comprehensive income	635								635
Issuance of stock	(238)		(238)
Common stock issued to dividend reinvestment plan and employee benefit plans	652			38		614
Common stock issued for acquisition	163,589			8,131		155,458
Amortization of restricted stock unit awards	1,683					1,683
Vesting of restricted stock unit awards, net of shares surrendered to cover payroll taxes	(643)			89	332	(1,064)
Purchases of common stock	0
Deferred compensation plan, net, including dividend equivalents	113				113
Common stock issued from deferred compensation plan, net of shares surrendered to cover payroll taxes	(129)			18	(459)	312
Preferred stock dividends	(1,814)						(1,814)
Common stock dividends	(15,845)						(15,845)
Ending balance at Sep. 30, 2020	$ 1,967,255		$ 96,422	$ 86,611	$ 10,632	$ 1,637,467	$ 94,938		$ 41,185