Earnings Per Share Reconciliation (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share Reconciliation
Number of participating securities outstanding (in shares)	0
NUMERATOR
Net income from continuing operations	$ 48,528	$ 53,558	$ 104,097	$ 306,793
Net income from discontinued operations	0	91	0	167
Less: distributed earnings allocated to nonvested restricted stock	0	(3)	0	(10)
Less: undistributed earnings allocated to nonvested restricted stock	0	(119)	(44)	(997)
Numerator for basic earnings per share	48,528	53,527	104,053	305,953
Plus: undistributed earnings allocated to nonvested restricted stock	0	119	44	997
Less: undistributed earnings reallocated to nonvested restricted stock	0	(96)	(35)	(824)
Numerator for diluted earnings per share	49,556	54,576	107,147	308,720
DENOMINATOR
Basic earnings per share-weighted-average shares	46,613,492	46,174,767	46,702,982	45,882,932
Effect of dilutive securities:
Share-based payments (in shares)	1,008,349	914,480	1,056,556	995,257
Diluted earnings per share-adjusted weighted-average shares and assumed conversions	58,211,583	57,678,989	58,349,280	55,658,536
NET INCOME PER COMMON SHARE
Basic (in dollars per share)	$ 1.04	$ 1.16	$ 2.23	$ 6.67
Diluted (in dollars per share)	$ 0.85	$ 0.95	$ 1.84	$ 5.55
1.6 percent convertible senior notes due 2018
NUMERATOR
Plus: interest on convertible senior notes	729	729	2,187	2,187
Effect of dilutive securities:
Convertible senior notes (in shares)	7,023,780	7,023,780	7,023,780	7,023,780
NET INCOME PER COMMON SHARE
Interest rate stated percentage	1.60%		1.60%
0.25 percent convertible senior notes due 2019
NUMERATOR
Plus: interest on convertible senior notes	$ 299	$ 297	$ 898	$ 407
Effect of dilutive securities:
Convertible senior notes (in shares)	3,565,962	3,565,962	3,565,962	1,756,567
NET INCOME PER COMMON SHARE
Interest rate stated percentage	0.25%		0.25%