Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by (used in) operating activities	$ 793,267	$ 797,948	$ 859,695
Net cash (used in) provided by investing activities	(274,106)	881,637	941,417
(Gain) loss on extinguishment and forgiveness of debt, net	(424,385)	(337,022)	(188,892)
Accounting Standards Update 2016-15 [Member] | Settlement Of Insurance Claims And Distributions Received From Equity Method Investments [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by (used in) operating activities		(2,600)	(6,500)
Net cash (used in) provided by investing activities		2,600	6,500
Accounting Standards Update 2016-15 [Member] | Proceeds From Settlement Of Insurance Claims [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by (used in) operating activities			(800)
Net cash (used in) provided by investing activities			800
Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase (decrease) in investing activities cash flows from restricted cash		(11,100)	1,500
(Gain) loss on extinguishment and forgiveness of debt, net		$ 3,600	$ 4,400
New Accounting Pronouncement, Early Adoption, Effect [Member] | Accounting Standards Update 2017-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Capitalized acquisition costs	$ 3,300