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		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share, Basic and Diluted [Line Items]
Net income (loss) - numerator for earnings (loss) per common share		$ (7,420)	$ 97,306	$ (37,553)	$ 186,054
Weighted average common shares outstanding (shares)	[1]	86,261,692	79,675,955	83,645,427	77,994,602
Effect of dilutive securities: 2015 warrants (shares)		0	714,980	20,219	766,795
Denominator for earnings (loss) per common share - assuming dilution		87,043,926	81,558,636	84,412,553	79,977,310
Earnings (loss) per common share		$ (0.09)	$ 1.22	$ (0.45)	$ 2.39
Earnings (loss) per common share - assuming dilution		$ (0.09)	$ 1.19	$ (0.45)	$ 2.33
Stock Options and Deferred Compensation Agreements [Member]
Earnings Per Share, Basic and Diluted [Line Items]
Effect of dilutive securities: share-based payment arrangements (shares)		424,875	981,271	423,498	1,076,166
Restricted Stock and Restricted Stock Units [Member]
Earnings Per Share, Basic and Diluted [Line Items]
Effect of dilutive securities: share-based payment arrangements (shares)		357,359	186,430	323,409	139,747

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