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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share Reconciliation
Net Income, Basic EPS	$ 457,251	$ (19,298)	$ 502,614	$ 120,461
Basic Shares Outstanding (in shares)	73,093	72,346	72,861	72,220
Earnings Per Share, Basic (in dollars per share)	$ 6.26	$ (0.27)	$ 6.90	$ 1.67
Effect of dilutive securities
Net Income, Diluted EPS	$ 457,251	$ (19,298)	$ 502,614	$ 120,461
Diluted Shares Outstanding (in shares)	73,507	72,346	73,238	72,272
Earnings Per Share, Diluted (dollars per share)	$ 6.22	$ (0.27)	$ 6.86	$ 1.67
Stock options
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	231	0	219	41
Non-vested restricted stock
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	68	0	67	10
Performance share awards
Effect of dilutive securities
Incremental common shares attributable to share-based payment arrangements	0	0	91	1