Consolidated Statements of Cash Flows - Supplemental Information (Reconciliation of Cash, Cash Equivalents and Restricted Cash) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 108,152	$ 148,929	$ 35,755	$ 35,687
Restricted cash	1,185	56,816	13,485	15,634
Total cash, cash equivalents, and restricted cash	$ 109,337	$ 205,745	$ 49,240	$ 51,321