Revenues and Business Information - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 item
Revenues From External Customers And Long Lived Assets [Line Items]
Deferred revenue	$ 7,074	$ 4,948
Revenues recognized from opening balance of deferred revenues	$ 4,948
Client | Revenue
Revenues From External Customers And Long Lived Assets [Line Items]
Number of clients | item	0	0	0