Basis of Presentation - Summary of Reconciliation of Cash, Cash Equivalents, and Restricted Cash Reported in the Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents, beginning of period	$ 233,711	$ 189,326
Cash and cash equivalents	195,515	178,068
Restricted cash, end of period	5,746	0
Cash, cash equivalents and restricted cash of $5,746 at end of period	201,261	178,068
Net decrease in cash, cash equivalents and restricted cash	$ (32,450)	$ (11,258)