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	157,130			157,130
Dividends — par value reduction	(12,981)	(12,981)
Dividends	(17,127)			(17,127)
Other comprehensive loss	0
Stock compensation	2,443		22,157	(19,714)
Share repurchases	(82,571)		(82,571)
Shares cancelled	0	(11,602)	82,571	(70,969)
Balance, at end of period at Jun. 30, 2013	3,373,229	430,397	(91,661)	3,034,493
Balance, at beginning of period at Dec. 31, 2013	3,519,826	418,988	(79,992)	3,180,830
Net income	328,835			328,835
Dividends	(38,345)			(38,345)
Other comprehensive loss	0
Stock compensation	11,978		14,734	(2,756)
Share repurchases	(139,532)		(139,532)
Shares cancelled	0	(16,081)	139,532	(123,451)
Balance, at end of period at Jun. 30, 2014	$ 3,682,762	$ 402,907	$ (65,258)	$ 3,345,113