Reconciliation of Earnings Per Share (EPS) - Earnings Per Share Reconciliation (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share Reconciliation
Net Income, Basic EPS	$ (19,298)	$ 2,046	$ 120,461	$ 190,739
Basic Shares Outstanding (in shares)	72,346	72,130	72,220	72,121
Earnings Per Share, Basic (in dollars per share)	$ (0.27)	$ 0.03	$ 1.67	$ 2.64
Effect of dilutive securities
Net Income, Diluted EPS	$ (19,298)	$ 2,046	$ 120,461	$ 190,739
Diluted Shares Outstanding (in shares)	72,346	72,316	72,272	72,301
Earnings Per Share, Diluted (dollars per share)	$ (0.27)	$ 0.03	$ 1.67	$ 2.64
Stock options
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	0	183	41	177
Non-vested restricted stock
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	0	3	10	3
Performance share awards
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements			1	0