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	88,347						88,347
Other comprehensive income	48,366								48,366
Exercise of stock options	197			12		185
Common stock issued to dividend reinvestment plan and employee benefit plans	1,091			42		1,049
Amortization of stock options and or restricted stock awards	6,002					6,002
Vesting of restricted stock, net of shares surrendered to cover payroll taxes	(392)			21	1,009	(1,422)
Purchases of common stock	(7,840)			(305)		(7,535)
Deferred compensation plan, net, including dividend equivalents	292				292
Shares issued from deferred compensation plan, net of shares surrendered to cover payroll taxes	(239)			71	(1,187)	877
Common stock dividends	(26,495)						(26,495)
Ending balance at Jun. 30, 2019	1,566,334		0	79,075	10,858	1,498,740	(29,116)		6,777
Beginning balance at Mar. 31, 2019	1,508,158		0	79,035	10,291	1,494,400	(59,573)		(15,995)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	44,085						44,085
Other comprehensive income	22,772								22,772
Exercise of stock options	0
Common stock issued to dividend reinvestment plan and employee benefit plans	905			34		871
Amortization of stock options and or restricted stock awards	4,017					4,017
Vesting of restricted stock, net of shares surrendered to cover payroll taxes	(75)			5	477	(557)
Purchases of common stock	0
Deferred compensation plan, net, including dividend equivalents	107				107
Shares issued from deferred compensation plan, net of shares surrendered to cover payroll taxes	(7)			1	(17)	9
Common stock dividends	(13,628)						(13,628)
Ending balance at Jun. 30, 2019	1,566,334		0	79,075	10,858	1,498,740	(29,116)		6,777
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	56,980						56,980
Other comprehensive income	32,156								32,156
Issuance of stock	96,660		96,660
Common stock issued to dividend reinvestment plan and employee benefit plans	426			22		404
Amortization of stock options and or restricted stock awards	4,256					4,256
Vesting of restricted stock, net of shares surrendered to cover payroll taxes	(679)			62	676	(1,417)
Purchases of common stock	(20,782)			(827)		(19,955)
Deferred compensation plan, net, including dividend equivalents	267				267
Shares issued from deferred compensation plan, net of shares surrendered to cover payroll taxes	(1,189)			64	(1,788)	535
Common stock dividends	(28,613)						(28,613)
Ending balance at Jun. 30, 2020	1,771,645		96,660	78,335	10,646	1,480,464	64,990		40,550
Beginning balance at Mar. 31, 2020	1,640,612		0	78,284	10,534	1,478,719	54,206		18,869
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	25,096						25,096
Other comprehensive income	21,681								21,681
Issuance of stock	96,660		96,660
Common stock issued to dividend reinvestment plan and employee benefit plans	227			13		214
Amortization of stock options and or restricted stock awards	1,764					1,764
Vesting of restricted stock, net of shares surrendered to cover payroll taxes	(191)			38	11	(240)
Purchases of common stock	0
Deferred compensation plan, net, including dividend equivalents	111				111
Shares issued from deferred compensation plan, net of shares surrendered to cover payroll taxes	(3)			0	(10)	7
Common stock dividends	(14,312)						(14,312)
Ending balance at Jun. 30, 2020	$ 1,771,645		$ 96,660	$ 78,335	$ 10,646	$ 1,480,464	$ 64,990		$ 40,550