Reconciliation of Earnings Per Share (EPS) - Earnings Per Share Reconciliation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share Reconciliation
Net Income (Loss), Basic EPS	$ (111,601)	$ (7,953)	$ (127,021)	$ 45,363
Basic Average Common Shares Outstanding (in shares)	73,452	72,851	73,143	72,737
Earnings Per Share, Basic (in dollars per share)	$ (1.52)	$ (0.11)	$ (1.74)	$ 0.62
Effect of dilutive securities
Net Income (Loss), Diluted EPS	$ (111,601)	$ (7,953)	$ (127,021)	$ 45,363
Diluted Average Common Shares Outstanding (in shares)	73,452	72,851	73,143	73,031
Earnings Per Share, Diluted (dollars per share)	$ (1.52)	$ (0.11)	$ (1.74)	$ 0.62
Stock options
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	0	0	0	165
Non-vested restricted stock
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	0	0	0	48
Performance share awards
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	0	0	0	81