Financial Instruments - Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Restricted cash, current	$ 28,657	$ 44,387
Restricted cash, non-current	31,100	32,397
Total restricted cash	59,757	76,784
Consolidated Entity, Excluding VIEs
Variable Interest Entity [Line Items]
Restricted cash, current	25,740	36,418
Restricted cash, non-current	3,246	5,649
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Restricted cash, current	2,917	7,969
Restricted cash, non-current	$ 27,854	$ 26,748