Reconciliation of Earnings Per Share (EPS) - Earnings Per Share Reconciliation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share Reconciliation
Net Income (Loss), Basic EPS	$ (227,904)	$ 457,251	$ (354,925)	$ 502,614
Basic Average Common Shares Outstanding (in shares)	78,742	73,093	75,125	72,861
Earnings Per Share, Basic (in dollars per share)	$ (2.89)	$ 6.26	$ (4.72)	$ 6.90
Effect of dilutive securities
Net Income (Loss), Diluted EPS	$ (227,904)	$ 457,251	$ (354,925)	$ 502,614
Diluted Average Common Shares Outstanding (in shares)	78,742	73,507	75,125	73,238
Earnings Per Share, Diluted (dollars per share)	$ (2.89)	$ 6.22	$ (4.72)	$ 6.86
Stock options
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	0	231	0	219
Non-vested restricted stock
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	0	68	0	67
Performance share awards
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	0	115	0	91