Summary of Significant Accounting Policies - Equity Statement (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained earnings, beginning		$ 2,343,878	$ 3,535,746	$ 3,741,316
Balance at beginning of period		1,323,329	2,398,169	2,628,755
Retained earnings, ending	$ 1,616,595	2,169,002	2,343,878	3,535,746
Balance at end of period	656,803	1,247,099	1,323,329	2,398,169
As Previously Reported
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained earnings, beginning		2,460,224	3,545,359	3,745,815
Balance at beginning of period		1,439,675	2,407,782	2,633,254
Retained earnings, ending	1,629,257	2,179,358	2,460,224	3,545,359
Balance at end of period	669,465	1,257,455	1,439,675	2,407,782
Adjustments
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained earnings, beginning		(116,346)	(9,613)	(4,499)
Balance at beginning of period		(116,346)	(9,613)	(4,499)
Retained earnings, ending	(12,662)	(10,356)	(116,346)	(9,613)
Balance at end of period	$ (12,662)	$ (10,356)	$ (116,346)	$ (9,613)