Commitments and Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2004	Dec. 31, 2002	Sep. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Local deals and getaway merchant payables			$ 7.1	$ 11.8
Travel Zoo Com Corporation
Business Acquisition [Line Items]
Period for receiving shares under merger (in years)	2 years	2 years
Number of shares exchanged under merger (in shares)		1