Basis of Presentation - Summary of Reconciliation of Cash, Cash Equivalents, and Restricted Cash Reported in the Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents, beginning of period	$ 233,711	$ 189,326
Cash and cash equivalents	230,259	185,516
Restricted cash, end of period	5,599	0
Cash, cash equivalents and restricted cash of $5,599 at end of period	235,858	185,516
Net increase (decrease) in cash, cash equivalents and restricted cash	$ 2,147	$ (3,810)