Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Current restricted cash	$ 39,430	$ 31,436
Non-current restricted cash	14,700	14,700
Held in Trust Deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Current restricted cash	30,700	29,300
Held for Advertising Activity Deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Current restricted cash	$ 8,600	$ 2,100