Significant Accounting Policies - Cash Reconciliation (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash Reconciliation [Abstract]
Cash and cash equivalents	$ 20,751	$ 22,058
Long-term restricted cash equivalents	6,336	6,336
Total cash, cash equivalents and restricted cash equivalents	$ 27,087	$ 28,394	$ 32,838	$ 111,897