Significant Accounting Policies (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share Reconciliation
Net earnings (loss)	$ 41,118,000	$ 63,910,000	$ 116,377,000	$ 16,433,000	$ (472,032,000)	$ (602,146,000)	$ (1,186,982,000)	$ 84,262,000	$ 237,838,000	$ (2,176,898,000)	$ 453,202,000
Weighted average common shares outstanding - basic									152,963,000	152,845,000	152,754,000
Effect of dilutive instruments									1,463,000	0	1,582,000
Weighted average common shares outstanding - fully diluted									154,426,000	152,845,000	154,336,000
Net (loss) income per common share - basic	$ 0.27	$ 0.42	$ 0.76	$ 0.11	$ (3.09)	$ (3.94)	$ (7.76)	$ 0.55	$ 1.55	$ (14.24)	$ 2.97
Net (loss) income per common share - fully diluted	$ 0.27	$ 0.41	$ 0.75	$ 0.11	$ (3.09)	$ (3.94)	$ (7.76)	$ 0.55	$ 1.54	$ (14.24)	$ 2.94
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount									1,406,000	1,900,000	1,030,000