Condensed Consolidated Statements of Shareholders Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]
Balance at Dec. 31, 2012	$ 3,163,699	$ 1,856	$ 1,226,835	$ 1,935,008
Balance, shares at Dec. 31, 2012	185,604,681
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	463,897			463,897
Stock-based compensation (unaudited)	19,003		19,003
Restricted stock:
Issued (unaudited)	1	1	0	0
Issued (unaudited), shares		129,850
Repurchased and canceled (unaudited)	(3,259)		(3,259)
Repurchased and canceled (unaudited), shares		(38,876)
Forfeited (unaudited), shares		(52,823)
Forfeitures (unaudited), value	(1)	(1)
Common Stock, Shares, Issued	185,642,832
Balance at Jun. 30, 2013	$ 3,643,340	$ 1,856	$ 1,242,579	$ 2,398,905
Balance, shares at Jun. 30, 2013	185,642,832