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, 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	163,042				163,042
Other Comprehensive Income (Loss)	5,137			5,137
Share-Based Compensation	7,870		7,870
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits	10,767	$ 2	1,557		(335)	9,543
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)		345,278
Common Stock Repurchased	(64,046)					(64,046)
Common Stock Repurchased (in shares)		(1,111,455)
Cash Dividends Declared ($1.80 per share)	(79,660)				(79,660)
Balance at End of Period at Dec. 31, 2014	1,055,086	$ 574	531,932	(26,686)	1,234,801	(685,535)
Ending Balance (in shares) at Dec. 31, 2014		43,724,208
Increase (decrease) in shareholders' equity
Net Income	160,704				160,704
Other Comprehensive Income (Loss)	3,129			3,129
Share-Based Compensation	7,689		7,689
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits	21,000	$ 1	2,420		(878)	19,457
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)		401,904
Common Stock Repurchased	(52,981)					(52,981)
Common Stock Repurchased (in shares)		(843,959)
Cash Dividends Declared ($1.80 per share)	(78,367)				(78,367)
Balance at End of Period at Dec. 31, 2015	$ 1,116,260	$ 575	542,041	(23,557)	1,316,260	(719,059)
Ending Balance (in shares) at Dec. 31, 2015	43,282,153	43,282,153
Increase (decrease) in shareholders' equity
Net Income	$ 181,461				181,461
Other Comprehensive Income (Loss)	(10,349)			(10,349)
Share-Based Compensation	6,786		6,786
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits	10,343	$ 1	2,801		(1,124)	8,665
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)		259,985
Common Stock Repurchased	$ (61,807)					(61,807)
Common Stock Repurchased (in shares)	(847,964)	(906,160)
Cash Dividends Declared ($1.80 per share)	$ (81,157)				(81,157)
Balance at End of Period at Dec. 31, 2016	$ 1,161,537	$ 576	$ 551,628	$ (33,906)	$ 1,415,440	$ (772,201)
Ending Balance (in shares) at Dec. 31, 2016	42,635,978	42,635,978