CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 30,043	$ 52,056	$ 40,225
Total cash, cash equivalents, and restricted cash shown in statement of cash flows	30,406	$ 52,419	40,682	$ 53,433
Prepaid expenses and other current assets
Restricted Cash and Cash Equivalents [Abstract]
Restricted cash	60		154
Other long-term assets
Restricted Cash and Cash Equivalents [Abstract]
Restricted cash	$ 303		$ 303