CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 44,349	$ 52,056	$ 43,272
Total cash, cash equivalents, and restricted cash shown in statement of cash flows	44,712	$ 52,419	43,905	$ 53,433
Prepaid expenses and other current assets
Restricted Cash and Cash Equivalents [Abstract]
Restricted cash	60		330
Other long-term assets
Restricted Cash and Cash Equivalents [Abstract]
Restricted cash	$ 303		$ 303