Unaudited Condensed Consolidated Statements Of Shareholders' Equity (USD $) In Thousands	Total	Common shares	Treasury Shares	Retained Earnings [Member]
Balance, at beginning of period at Dec. 31, 2012	$ 3,326,335	$ 454,980	$ (113,818)	$ 2,985,173
Net income	158,992			158,992
Dividends — par value reduction	(12,981)	(12,981)
Other comprehensive loss	0
Stock compensation	(4,138)		17,465	(21,603)
Share repurchases	(36,245)		(36,245)
Shares cancelled	0	(5,412)	36,245	(30,833)
Balance, at end of period at Mar. 31, 2013	3,431,963	436,587	(96,353)	3,091,729
Balance, at beginning of period at Dec. 31, 2013	3,519,826	418,988	(79,992)	3,180,830
Net income	176,972			176,972
Dividends	(16,489)			(16,489)
Other comprehensive loss	0
Stock compensation	5,028		11,236	(6,208)
Share repurchases	(68,659)		(68,659)
Shares cancelled	0	(8,168)	68,659	(60,491)
Balance, at end of period at Mar. 31, 2014	$ 3,616,678	$ 410,820	$ (68,756)	$ 3,274,614