Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Adoption of new accounting standard	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)	$ 79,234	$ 10,744	$ 1,499,584	$ (90,419)	$ (549)	$ (41,589)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	44,262					44,262
Other comprehensive income	25,594							25,594
Exercise of stock options	197		12		185
Common stock issued to dividend reinvestment plan and employee benefit plans	186		8		178
Amortization of stock options and or restricted stock awards	1,985				1,985
Vesting of restricted stock, net of shares surrendered to cover payroll taxes	(317)		16	532	(865)
Purchases of common stock	(7,840)		(305)		(7,535)
Deferred compensation plan, net, including dividend equivalents	185			185
Shares issued from deferred compensation plan, net of shares surrendered to cover payroll taxes	(232)		70	(1,170)	868
Common stock dividends	(12,867)					(12,867)
Ending balance at Mar. 31, 2019	1,508,158		79,035	10,291	1,494,400	(59,573)		(15,995)
Beginning balance at Dec. 31, 2019	1,635,692	$ (3,529)	79,014	11,491	1,496,641	40,152	$ (3,529)	8,394
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	31,884					31,884
Other comprehensive income	10,475							10,475
Common stock issued to dividend reinvestment plan and employee benefit plans	199		9		190
Amortization of stock options and or restricted stock awards	2,492				2,492
Vesting of restricted stock, net of shares surrendered to cover payroll taxes	(488)		24	665	(1,177)
Purchases of common stock	(20,782)		(827)		(19,955)
Deferred compensation plan, net, including dividend equivalents	156			156
Shares issued from deferred compensation plan, net of shares surrendered to cover payroll taxes	(1,186)		64	(1,778)	528
Common stock dividends	(14,301)					(14,301)
Ending balance at Mar. 31, 2020	$ 1,640,612		$ 78,284	$ 10,534	$ 1,478,719	$ 54,206		$ 18,869