Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Capital Surplus	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Balance at Beginning of Period at Dec. 31, 2016	$ 1,161,537	$ 576	$ 551,628	$ (33,906)	$ 1,415,440	$ (772,201)
Beginning Balance (in shares) at Dec. 31, 2016		42,635,978
Increase (decrease) in shareholders' equity
Net Income	184,672				184,672
Other Comprehensive Income (Loss)	(809)			(809)
Share-Based Compensation	7,369		7,369
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits	13,241	$ 0	2,164		(828)	11,905
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)		337,091
Common Stock Repurchased	(47,076)					(47,076)
Common Stock Repurchased (in shares)		(571,626)
Cash Dividends Declared	87,066				87,066
Balance at End of Period at Dec. 31, 2017	1,231,868	$ 576	561,161	(34,715)	1,512,218	(807,372)
Ending Balance (in shares) at Dec. 31, 2017		42,401,443
Increase (decrease) in shareholders' equity
Net Income	219,602				219,602
Other Comprehensive Income (Loss)	(8,851)			(8,851)
Reclassification of the Income Tax Effect of the Tax Reform from AOCI to RE				(7,477)	7,477
Share-Based Compensation	8,146		8,146
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits	7,919	$ 1	2,397		513	5,008
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)		219,210
Common Stock Repurchased	(91,988)					(91,988)
Common Stock Repurchased (in shares)		(1,120,755)
Cash Dividends Declared	98,496				98,496
Balance at End of Period at Dec. 31, 2018	$ 1,268,200	$ 577	571,704	(51,043)	1,641,314	(894,352)
Ending Balance (in shares) at Dec. 31, 2018	41,499,898	41,499,898
Increase (decrease) in shareholders' equity
Net Income	$ 225,913				225,913
Other Comprehensive Income (Loss)	19,931			19,931
Share-Based Compensation	8,337		8,337
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits	7,578	$ 2	2,525		(334)	5,385
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)		212,924
Common Stock Repurchased	$ (137,649)					(137,649)
Common Stock Repurchased (in shares)	(1,642,998)	(1,673,127)
Cash Dividends Declared	$ 105,478				105,478
Balance at End of Period at Dec. 31, 2019	$ 1,286,832	$ 579	$ 582,566	$ (31,112)	$ 1,761,415	$ (1,026,616)
Ending Balance (in shares) at Dec. 31, 2019	40,039,695	40,039,695