Supplemental Disclosures Supplemental Disclosures - Restricted Cash Reconciliation (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash	$ 27,030	$ 96,505	$ 209,705
Restricted cash	25,753	5,977	14,604
Total cash and restricted cash	$ 52,783	$ 102,482	$ 224,309	$ 214,142