Earnings Per Share Reconciliation (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Jun. 30, 2013	Dec. 31, 2012
NUMERATOR
Net income from continuing operations	$ 53,558	$ 10,407	$ 306,793	$ 13,435
Net income (loss) from discontinued operations	91	238	167	(1,626)
Less: distributed earnings allocated to nonvested restricted stock	(3)	(10)	(10)	(32)
Less: undistributed earnings allocated to nonvested restricted stock	(119)	(69)	(997)	(73)
Numerator for basic income (loss) per share	53,527	10,566	305,953	11,704
Plus: undistributed earnings allocated to nonvested restricted stock	119	69	997	73
Less: undistributed earnings reallocated to nonvested restricted stock	(96)	(59)	(824)	(74)
Numerator for diluted income (loss) per share	54,576	11,305	308,720	11,703
DENOMINATOR
Basic earnings per share-weighted-average shares	46,174,767	44,825,943	45,882,932	44,643,139
Effect of dilutive securities:
Share-based payments (in shares)	914,480	616,047	995,257	336,769
Diluted earnings per share-adjusted weighted-average shares and assumed conversions	57,678,989	52,465,770	55,658,536	44,979,908
Basic
Continuing operations (in dollars per share)	$ 1.16	$ 0.23	$ 6.67	$ 0.30
Discontinued operations (in dollars per share)	$ 0.00	$ 0.01	$ 0.00	$ (0.04)
Total (in dollars per share)	$ 1.16	$ 0.24	$ 6.67	$ 0.26
Diluted
Continuing operations (in dollars per share)	$ 0.95	$ 0.21	$ 5.55	$ 0.30
Discontinued operations (in dollars per share)	$ 0.00	$ 0.01	$ 0.00	$ (0.04)
Total (in dollars per share)	$ 0.95	$ 0.22	$ 5.55	$ 0.26
1.6 percent convertible senior notes due 2018
NUMERATOR
Plus: interest on convertible senior notes	729	729	2,187	0
Effect of dilutive securities:
Convertible senior notes (in shares)	7,023,780	7,023,780	7,023,780	0
Diluted
Interest rate stated percentage	1.60%		1.60%
0.25 percent convertible senior notes due 2019
NUMERATOR
Plus: interest on convertible senior notes	$ 297	$ 0	$ 407	$ 0
Effect of dilutive securities:
Convertible senior notes (in shares)	3,565,962	0	1,756,567	0
Diluted
Interest rate stated percentage	0.25%		0.25%		0.25%	0.25%