Summary of Significant Accounting Policies - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash in Accompanying Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2019		Dec. 31, 2018	Jun. 30, 2018		Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 130,510		$ 280,587	$ 342,925
Restricted cash	$ 113,680
Restricted cash included in other assets				$ 1,006
Restricted Cash and Cash Equivalents, Noncurrent, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent			us-gaap:OtherAssetsNoncurrent
Cash and cash equivalents, restricted cash	$ 244,190	[1]	$ 281,606	$ 343,931	[1]	$ 260,820

[1] See Note 2 of the accompanying notes for a reconciliation of the ending balance of cash, cash equivalents and restricted cash shown in these condensed consolidated statements of cash flows.