Basis of Presentation and Consolidation - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 180,493	$ 371,684	$ 302,386	$ 504,423
Restricted cash included in Other current assets	1,702	19,200	614	18,499
Restricted cash included in Other assets	2,090	1,422	1,337	1,327
Total cash, cash equivalents and restricted cash	$ 184,285	$ 392,306	$ 304,337	$ 524,249