Significant Accounting Policies (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share Reconciliation
Net earnings (loss)	$ 209,730	$ 125,357	$ 106,049	$ 101,715	$ 41,118	$ 63,910	$ 116,377	$ 16,433	$ 542,851	$ 237,838	$ (2,176,898)
Weighted average common shares outstanding - basic									153,136,000	152,963,000	152,845,000
Effect of dilutive instruments									1,558,000	1,463,000	0
Weighted average common shares outstanding - fully diluted									154,694,000	154,426,000	152,845,000
Net (income (loss) per common share - basic	$ 1.37	$ 0.82	$ 0.69	$ 0.66	$ 0.27	$ 0.42	$ 0.76	$ 0.11	$ 3.54	$ 1.55	$ (14.24)
Net income (loss) per common share - fully diluted	$ 1.36	$ 0.81	$ 0.68	$ 0.66	$ 0.27	$ 0.41	$ 0.75	$ 0.11	$ 3.51	$ 1.54	$ (14.24)
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount									1,377,000	1,406,000	1,900,000