Summary of Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and cash equivalents	$ 196,981	$ 5,409
Restricted cash	0	49,098
Total cash, cash equivalents and restricted cash	$ 196,981	$ 54,507	$ 12,649	$ 4,102