Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Capital Surplus	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock	CECL Adoption Impact	CECL Adoption Impact Retained Earnings
Beginning Balance (in shares) at Dec. 31, 2018		41,499,898
Balance at Beginning of Period at Dec. 31, 2018	$ 1,268,200	$ 577	$ 571,704	$ (51,043)	$ 1,641,314	$ (894,352)
Increase (decrease) in shareholders' equity
Net Income	58,799				58,799
Other Comprehensive Income	7,165			7,165
Share-Based Compensation	2,274		2,274
Common Stock Issued under Purchase and Equity Compensation Plans	2,087	$ 1	616		(203)	1,673
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)		131,529
Common Stock Repurchased	(43,189)					(43,189)
Common Stock Repurchased (in shares)		(552,739)
Cash Dividends Declared (per share)	(25,646)				(25,646)
Balance at End of Period at Mar. 31, 2019	1,269,690	$ 578	574,594	(43,878)	1,674,264	(935,868)
Ending Balance (in shares) at Mar. 31, 2019		41,078,688
Beginning Balance (in shares) at Dec. 31, 2018		41,499,898
Balance at Beginning of Period at Dec. 31, 2018	1,268,200	$ 577	571,704	(51,043)	1,641,314	(894,352)
Increase (decrease) in shareholders' equity
Net Income	115,718
Other Comprehensive Income	23,619			23,619
Balance at End of Period at Jun. 30, 2019	1,285,948	$ 579	577,346	(27,424)	1,704,993	(969,546)
Ending Balance (in shares) at Jun. 30, 2019		40,687,719
Beginning Balance (in shares) at Mar. 31, 2019		41,078,688
Balance at Beginning of Period at Mar. 31, 2019	1,269,690	$ 578	574,594	(43,878)	1,674,264	(935,868)
Increase (decrease) in shareholders' equity
Net Income	56,919				56,919
Other Comprehensive Income	16,454			16,454
Share-Based Compensation	2,164		2,164
Common Stock Issued under Purchase and Equity Compensation Plans	2,262	$ 1	588		365	1,308
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)		43,180
Common Stock Repurchased	(34,986)					34,986
Common Stock Repurchased (in shares)		(434,149)
Cash Dividends Declared (per share)	(26,555)				(26,555)
Balance at End of Period at Jun. 30, 2019	$ 1,285,948	$ 579	577,346	(27,424)	1,704,993	(969,546)
Ending Balance (in shares) at Jun. 30, 2019		40,687,719
Increase (decrease) in shareholders' equity
Cumulative Change in Accounting Principle							$ 3,632	$ 3,632
Beginning Balance (in shares) at Dec. 31, 2019	40,039,695	40,039,695
Balance at Beginning of Period at Dec. 31, 2019	$ 1,286,832	$ 579	582,566	(31,112)	1,761,415	(1,026,616)
Increase (decrease) in shareholders' equity
Net Income	34,742				34,742
Other Comprehensive Income	41,933			41,933
Share-Based Compensation	1,497		1,497
Common Stock Issued under Purchase and Equity Compensation Plans	3,761	$ 0	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
Beginning Balance (in shares) at Dec. 31, 2019	40,039,695	40,039,695
Balance at Beginning of Period at Dec. 31, 2019	$ 1,286,832	$ 579	582,566	(31,112)	1,761,415	(1,026,616)
Increase (decrease) in shareholders' equity
Net Income	73,650
Other Comprehensive Income	50,037			50,037
Balance at End of Period at Jun. 30, 2020	$ 1,352,082	$ 580	586,946	18,925	1,786,351	(1,040,720)
Ending Balance (in shares) at Jun. 30, 2020	40,047,694	40,047,694
Beginning Balance (in shares) at Mar. 31, 2020		39,996,510
Balance at Beginning of Period at Mar. 31, 2020	$ 1,327,929	$ 579	584,392	10,821	1,773,607	(1,041,470)
Increase (decrease) in shareholders' equity
Net Income	38,908				38,908
Other Comprehensive Income	8,104			8,104
Share-Based Compensation	2,207		2,207
Common Stock Issued under Purchase and Equity Compensation Plans	1,926	$ 1	347		680	898
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)		53,672
Common Stock Repurchased	(148)					(148)
Common Stock Repurchased (in shares)		(2,488)
Cash Dividends Declared (per share)	(26,844)				(26,844)
Balance at End of Period at Jun. 30, 2020	$ 1,352,082	$ 580	$ 586,946	$ 18,925	$ 1,786,351	$ (1,040,720)
Ending Balance (in shares) at Jun. 30, 2020	40,047,694	40,047,694