Basis of Presentation - Cash and Restricted Cash Equivalents (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 102,402	$ 119,094
Restricted cash	27,083	26,014
Total cash and cash equivalents, and restricted cash	$ 129,485	$ 145,108	$ 230,501	$ 300,153