Earnings (Loss) Per Share and Stockholders' Equity (Schedule of Earnings (Loss) Per Share, Basic and Diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share, Basic and Diluted [Line Items]
Net income (loss) - numerator for earnings (loss) per common share		$ 14,708	$ 82,845	$ (30,133)	$ 88,748
Weighted average common shares outstanding (shares)	[1]	82,516,927	77,237,200	82,322,919	77,139,992
Effect of dilutive securities: 2015 warrants (shares)		0	779,926	30,439	793,132
Denominator for earnings (loss) per common share - assuming dilution		83,184,137	79,227,317	83,072,816	79,173,143
Earnings (loss) per common share		$ 0.18	$ 1.07	$ (0.37)	$ 1.15
Earnings (loss) per common share - assuming dilution		$ 0.18	$ 1.05	$ (0.37)	$ 1.12
Stock Options and Deferred Compensation Agreements [Member]
Earnings Per Share, Basic and Diluted [Line Items]
Effect of dilutive securities: share-based payment arrangements (shares)		353,052	1,087,893	422,809	1,123,614
Restricted Stock and Restricted Stock Units [Member]
Earnings Per Share, Basic and Diluted [Line Items]
Effect of dilutive securities: share-based payment arrangements (shares)		314,158	122,298	296,649	116,405

[1] Weighted average common shares outstanding include shares vested under the NMO Deferred Compensation Plan.