Significant Accounting Policies - Summary of reconciliation of weighted average shares outstanding along with earnings per share attributable to restricted shares of common stock (Details 1) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Significant Accounting Policies
Net income (loss) available for stockholders	$ 175,402	$ 162,511	$ (141,246)
Less: Adjustments for losses attributable to participating securities	(1,839)	(2,102)	(147)
Net income (loss) used in calculating per share amounts	$ 173,563	$ 160,409	$ (141,393)
Weighted average shares outstanding (including participating securities)	215,198	217,194	217,509
Adjustment for participating securities	(2,453)	(2,891)	(3,282)
Shares used in calculating basic and diluted earnings (loss) per share	212,745	214,303	214,227