Supplemental Cash Flow Information of the Company - Cash and 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	$ 57,649	$ 193,418	$ 56,508	$ 23,781
Restricted cash	9,149	56,711	696	75,185
Cash and cash equivalents and restricted cash	$ 66,798	$ 250,129	$ 57,204	$ 98,966