Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In-Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Deferred Compensation Trust [Member]	Deferred Compensation Liability [Member]
Beginning Balance at Dec. 31, 2013	$ 1,261,352	$ 206	$ 1,212,050	$ 4,605,557	$ (4,556,461)	$ (17,741)	$ 17,741
Net income	281,630			281,630
Deferred compensation activity						408	(408)
Purchase of common stock for treasury	(567,544)				(567,544)
Equity-based compensation	63,227		63,227
Tax benefit from equity benefit plan activity	9,437		9,437
Proceeds from stock options exercised	76,153		76,153
Treasury stock issued upon option exercise and restricted share vesting			(35,372)		35,372
Ending Balance at Dec. 31, 2014	1,124,255	206	1,325,495	4,887,187	(5,088,633)	(17,333)	17,333
Net income	382,927			382,927
Purchase of common stock for treasury	(431,367)				(431,367)
Equity-based compensation	54,091		54,091
Tax benefit from equity benefit plan activity	23,311		23,311
Proceeds from stock options exercised	85,948		85,948
Treasury stock issued upon option exercise and restricted share vesting			(41,050)		41,050
Ending Balance at Dec. 31, 2015	1,239,165	206	1,447,795	5,270,114	(5,478,950)	(17,333)	17,333
Net income	425,262			425,262
Deferred compensation activity						(42)	42
Purchase of common stock for treasury	(455,351)				(455,351)
Equity-based compensation	43,598		43,598
Tax benefit from equity benefit plan activity	13,661		13,661
Proceeds from stock options exercised	38,106		38,106
Treasury stock issued upon option exercise and restricted share vesting			(27,332)		27,332
Ending Balance at Dec. 31, 2016	$ 1,304,441	$ 206	$ 1,515,828	$ 5,695,376	$ (5,906,969)	$ (17,375)	$ 17,375