FAIR VALUE MEASUREMENT - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) (Recurring, USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets measured at fair value:
Total assets measured at fair value	$ 8,813	$ 1,880
Money market funds
Assets measured at fair value:
Cash and cash equivalents	7,007	5
Restricted cash	1,806	1,875
Fair value measurements at reporting date, level 1
Assets measured at fair value:
Total assets measured at fair value	8,813	1,880
Fair value measurements at reporting date, level 1 | Money market funds
Assets measured at fair value:
Cash and cash equivalents	7,007	5
Restricted cash	$ 1,806	$ 1,875