Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Current restricted cash	$ 32,391	$ 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	31,200	29,300
Held for Advertising Activity Deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Current restricted cash	$ 1,200	$ 2,100