Significant Accounting Policies - Summary of reconciliation of weighted average shares outstanding along with earnings per share attributable to restricted shares of common stock (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Significant Accounting Policies
Net (loss) income available for stockholders	$ (141,246)	$ (99,561)	$ 245,193
Less: Adjustments for losses attributable to participating securities	(147)	(240)	(3,913)
Net loss used in calculating losses per share	$ (141,393)	$ (99,801)	$ 241,280
Weighted average shares outstanding (including participating securities)	217,509	213,632	214,840
Adjustment for participating securities	(3,282)	(3,359)	(3,632)
Shares used in calculating basic losses per share	214,227	210,273	211,208
Dilutive effect of stock based awards			1,049
Shares used in calculating diluted losses per share	214,227	210,273	212,257