Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Capital Surplus	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Treasury Stock
Balance at Beginning of Period at Dec. 31, 2019	$ 1,286,832	$ 3,632	$ 579	$ 582,566	$ (31,112)	$ 1,761,415	$ 3,632	$ (1,026,616)
Beginning Balance (in shares) at Dec. 31, 2019			40,039,695
Increase (decrease) in shareholders' equity
Net Income	34,742					34,742
Other Comprehensive Income (Loss)	$ 41,933				41,933
Accounting Standards Update Extensible List	Accounting Standards Update 2016-13
Share-Based Compensation	$ 1,497			1,497
Common Stock Issued under Purchase and Equity Compensation Plans	3,761			329		653		2,779
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)			154,091
Common Stock Repurchased	(17,633)							(17,633)
Common Stock Repurchased (in shares)			(197,276)
Cash Dividends Declared (per share)	(26,835)					(26,835)
Balance at End of Period at Mar. 31, 2020	1,327,929		$ 579	584,392	10,821	1,773,607		(1,041,470)
Ending Balance (in shares) at Mar. 31, 2020			39,996,510
Balance at Beginning of Period at Dec. 31, 2020	$ 1,374,507		$ 580	591,360	7,822	1,811,979		(1,037,234)
Beginning Balance (in shares) at Dec. 31, 2020	40,119,312		40,119,312
Increase (decrease) in shareholders' equity
Net Income	$ 59,949					59,949
Other Comprehensive Income (Loss)	(49,609)				(49,609)
Share-Based Compensation	2,780			2,780
Common Stock Issued under Purchase and Equity Compensation Plans	2,809			664		(845)		2,990
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)			310,905
Common Stock Repurchased	(3,189)							(3,189)
Common Stock Repurchased (in shares)			(35,983)
Cash Dividends Declared (per share)	(27,026)					(27,026)
Balance at End of Period at Mar. 31, 2021	$ 1,360,221		$ 580	$ 594,804	$ (41,787)	$ 1,844,057		$ (1,037,433)
Ending Balance (in shares) at Mar. 31, 2021	40,394,234		40,394,234