Summary of Significant Accounting Policies (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Current period net income	$ 125,867	$ (97,421)	$ (679,785)
Weighted average common shares outstanding — denominator
Weighted average common shares outstanding for basic earnings (loss) per share (in shares)	102,029,000	91,273,000	81,537,000
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	514,000	0	0
Diluted weighted average common shares outstanding (in shares)	102,543,000	91,273,000	81,537,000
Earnings (loss) per common share
Basic (usd per share)	$ 1.23	$ (1.07)	$ (8.34)
Diluted (usd per share)	$ 1.23	$ (1.07)	$ (8.34)
Stock options [Member]
Earnings (loss) per common share
Total (usd per share)	1,000,000	2,886,821	2,362,861
Restricted Stock Units (RSUs) [Member]
Earnings (loss) per common share
Total (usd per share)		90,552	73,923
Restricted stock [Member]
Earnings (loss) per common share
Total (usd per share)		1,039,292	854,238

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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