Earnings Per Share - Computation of Basic and Diluted EPS (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Basic:
Net income (loss) applicable to common shareholders	$ (403,867)	$ 9,880	$ (2,635)	$ 19,642	$ 7,960	$ 75,586	$ 57,782	$ 53,719	$ (376,980)	$ 195,047	$ 109,922
Less: Income from discontinued operations, net of tax									0	0	(1,073)
Net income (loss) from continuing operations									(376,980)	195,047	108,849
Less: Undistributed income allocable to participating securities – continuing operations									0	(1,018)	(801)
Net income (loss) applicable to common shareholders – continuing operations									$ (376,980)	$ 194,029	$ 108,048
Weighted average number of shares outstanding - basic (in shares)									105,416	105,029	105,032
Diluted:
Net income (loss) applicable to common shareholders – continuing operations									$ (376,980)	$ 194,029	$ 108,048
Effect of dilutive securities:
Share-based awards other than participating securities (in shares)									0	16	152
Undistributed income reallocated to participating securities									$ 0	$ 0	$ 1
Net income (loss) applicable to common shareholders – continuing operations									$ (376,980)	$ 194,029	$ 108,049
Weighted average number of shares outstanding, diluted									105,416	105,045	105,184
Discontinued operations:
Income from discontinued operations, net of tax									$ 0	$ 0	$ 1,073
Less: Undistributed income allocable to participating securities – discontinued operations									0	0	(8)
Net income applicable to common shareholders – discontinued operations									$ 0	$ 0	$ 1,065