Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Data (Unaudited)
Total revenues	$ 103,567	$ 123,667	$ 123,690	$ 120,247	$ 141,775	$ 146,000	$ 145,549	$ 142,472	$ 471,171	$ 575,796	$ 569,409
Income (loss) before income taxes and income from and impairment of equity method investment	(105,262)	58,693	83,799	61,397	(63,675)	79,634	76,271	23,133	98,627	115,363	296,594
Net income	$ (104,730)	$ 53,520	$ 83,593	$ 48,762	$ (88,672)	$ 74,990	$ 89,908	$ 36,967	$ 81,145	$ 113,193	$ 293,043
Earnings per common share, basic and diluted	$ (1.12)	$ 0.57	$ 0.89	$ 0.52	$ (0.95)	$ 0.80	$ 0.96	$ 0.39	$ 0.87	$ 1.21	$ 3.13