CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 50,750	$ 52,056	$ 49,640
Cash, cash equivalents and restricted cash at end of period	51,113	$ 52,419	50,279	$ 53,433
Prepaide expenses and other current assets
Restricted Cash and Cash Equivalents [Abstract]
Restricted cash	60		285
Other long-term assets
Restricted Cash and Cash Equivalents [Abstract]
Restricted cash	$ 303		$ 354