Supplemental Cash Flow and Other Information - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 56,352	$ 87,878	$ 107,138
Restricted cash included in other current assets	9,108	7,421	17,485
Cash, cash equivalents and restricted cash	$ 65,460	$ 95,299	$ 124,623	$ 85,052