Summary of Significant Accounting Policies - Revision of Previously Issued Comprehensive Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended	9 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	Jun. 30, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)	$ 1,530	$ 20,701	$ 43,063	$ 654	$ (121,173)	$ 32,121	$ 227,160	$ (8,215)	$ 218,945	$ 251,066	$ 65,948	$ 129,893	$ (92,144)
Net comprehensive income						29,814	228,110	(3,108)	217,447	247,261	$ 66,781	125,307	$ (90,708)
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)					(120,236)	40,845	228,101	(7,555)	220,546	261,391		141,155
Net comprehensive income						38,538	229,051	(2,448)	219,048	257,586		136,569
2015 Insurance Reserve | Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)					$ (937)	(8,724)	(941)	(660)	(1,601)	(10,325)		(11,262)
Net comprehensive income						$ (8,724)	$ (941)	$ (660)	$ (1,601)	$ (10,325)		$ (11,262)