Supplemental Disclosures Supplemental Disclosures - Restricted Cash Reconciliation (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash	$ 122,450	$ 96,505	$ 131,467
Restricted cash	21,063	5,977	15,040
Total cash and restricted cash	$ 143,513	$ 102,482	$ 146,507	$ 214,142