Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Cash and cash equivalents	$ 52,147	$ 67,111	$ 76,815
Restricted cash	5,213	6,101	4,581
Total cash, cash equivalents, and restricted cash	$ 57,360	$ 73,212	$ 81,396	$ 77,148