Earnings Per Share Reconciliation (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
NUMERATOR
Net income from continuing operations	$ 231,231	$ 6,049	$ 253,235	$ 3,028
Net (loss) income from discontinued operations	(37)	223	76	(1,864)
Less: distributed earnings allocated to nonvested restricted stock	(3)	(10)	(7)	0
Less: undistributed earnings allocated to nonvested restricted stock	(543)	(40)	(954)	0
Numerator for basic income (loss) per share	230,648	6,222	252,350	1,164
Plus: undistributed earnings allocated to nonvested restricted stock	543	40	954	0
Less: undistributed earnings reallocated to nonvested restricted stock	(450)	(37)	(803)	0
Numerator for diluted income (loss) per share	231,580	6,595	254,069	1,164
DENOMINATOR
Basic earnings per share-weighted-average shares	46,035,775	44,627,548	45,736,648	44,551,441
Effect of dilutive securities:
Share-based payments (in shares)	1,024,134	293,819	1,001,655	387,331
Diluted earnings per share-adjusted weighted-average shares and assumed conversions	55,690,331	48,394,665	54,569,842	44,938,772
Basic
Continuing operations (in dollars per share)	$ 5.01	$ 0.14	$ 5.52	$ 0.07
Discontinued operations (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ (0.04)
Total (in dollars per share)	$ 5.01	$ 0.14	$ 5.52	$ 0.03
Diluted
Continuing operations (in dollars per share)	$ 4.16	$ 0.14	$ 4.66	$ 0.07
Discontinued operations (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ (0.04)
Total (in dollars per share)	$ 4.16	$ 0.14	$ 4.66	$ 0.03
1.6 percent convertible senior notes due May 2018
NUMERATOR
Plus: interest on convertible senior notes	729	370	1,458	0
Effect of dilutive securities:
Convertible senior notes (in shares)	7,023,780	3,473,298	7,023,780	0
Diluted
Interest rate stated percentage	1.60%	1.60%	1.60%	1.60%
0.25 percent convertible senior notes due 2019
NUMERATOR
Plus: interest on convertible senior notes	$ 110	$ 0	$ 110	$ 0
Effect of dilutive securities:
Convertible senior notes (in shares)	1,606,642	0	807,759	0
Diluted
Interest rate stated percentage	0.25%		0.25%