Summary of Significant Accounting Policies - Cash and cash equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Cash and cash equivalents	$ 5,409	$ 4,102	$ 3,519
Restricted cash	49,098	0	0
Total cash, cash equivalents and restricted cash	$ 54,507	$ 4,102	$ 3,519	$ 8,671