Consolidated Statements of Shareholders' Equity (Unaudited) - 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, 2013	$ 1,011,976	$ 572	$ 522,505	$ (31,823)	$ 1,151,754	$ (631,032)
Beginning Balance (in shares) at Dec. 31, 2013		44,490,385
Increase (decrease) in shareholders' equity
Net Income	121,851				121,851
Other Comprehensive Income (Loss)	15,760			15,760
Share-Based Compensation	5,831		5,831
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits	8,853	$ 1	1,194		(318)	7,976
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)		314,579
Common Stock Repurchased	(46,910)					(46,910)
Common Stock Repurchased (in shares)		(811,235)
Cash Dividends Declared ($1.35 per share)	(59,948)				(59,948)
Balance at End of Period at Sep. 30, 2014	1,057,413	$ 573	529,530	(16,063)	1,213,339	(669,966)
Ending Balance (in shares) at Sep. 30, 2014		43,993,729
Balance at Beginning of Period at Jun. 30, 2014				(16,623)
Increase (decrease) in shareholders' equity
Net Income	41,769
Other Comprehensive Income (Loss)	560			560
Balance at End of Period at Sep. 30, 2014	1,057,413	$ 573	529,530	(16,063)	1,213,339	(669,966)
Ending Balance (in shares) at Sep. 30, 2014		43,993,729
Balance at Beginning of Period at Dec. 31, 2014	$ 1,055,086	$ 574	531,932	(26,686)	1,234,801	(685,535)
Beginning Balance (in shares) at Dec. 31, 2014	43,724,208	43,724,208
Increase (decrease) in shareholders' equity
Net Income	$ 117,872				117,872
Other Comprehensive Income (Loss)	5,394			5,394
Share-Based Compensation	5,698		5,698
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits	12,118	$ 1	1,482		(376)	11,011
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)		246,851
Common Stock Repurchased	(38,933)					(38,933)
Common Stock Repurchased (in shares)		(628,119)
Cash Dividends Declared ($1.35 per share)	(58,881)				(58,881)
Balance at End of Period at Sep. 30, 2015	$ 1,098,354	$ 575	539,112	(21,292)	1,293,416	(713,457)
Ending Balance (in shares) at Sep. 30, 2015	43,342,940	43,342,940
Balance at Beginning of Period at Jun. 30, 2015				(28,562)
Increase (decrease) in shareholders' equity
Net Income	$ 34,276
Other Comprehensive Income (Loss)	7,270			7,270
Balance at End of Period at Sep. 30, 2015	$ 1,098,354	$ 575	$ 539,112	$ (21,292)	$ 1,293,416	$ (713,457)
Ending Balance (in shares) at Sep. 30, 2015	43,342,940	43,342,940