Revenue - Summary (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue
Revenue	$ 122,517	$ 140,891	$ 234,035	$ 269,173
Direct
Revenue
Revenue	75,890		144,086
Tech-enabled
Revenue
Revenue	38,471		73,547
Traditional
Revenue
Revenue	8,156		16,402
North America
Revenue
Revenue	77,656	79,825	147,621	153,200
North America | Direct
Revenue
Revenue	40,109		75,221
North America | Tech-enabled
Revenue
Revenue	29,391		55,998
North America | Traditional
Revenue
Revenue	8,156		16,402
Europe
Revenue
Revenue	44,861	61,066	86,414	115,973
Europe | Direct
Revenue
Revenue	35,781		68,865
Europe | Tech-enabled
Revenue
Revenue	$ 9,080		$ 17,549
Presented without adoption of ASC 606
Revenue
Revenue		140,891		269,173
Presented without adoption of ASC 606 | Direct
Revenue
Revenue		86,941		167,140
Presented without adoption of ASC 606 | Tech-enabled
Revenue
Revenue		43,617		81,527
Presented without adoption of ASC 606 | Traditional
Revenue
Revenue		10,333		20,506
Presented without adoption of ASC 606 | North America
Revenue
Revenue		79,825		153,200
Presented without adoption of ASC 606 | North America | Direct
Revenue
Revenue		39,290		76,792
Presented without adoption of ASC 606 | North America | Tech-enabled
Revenue
Revenue		30,202		55,902
Presented without adoption of ASC 606 | North America | Traditional
Revenue
Revenue		10,333		20,506
Presented without adoption of ASC 606 | Europe
Revenue
Revenue		61,066		115,973
Presented without adoption of ASC 606 | Europe | Direct
Revenue
Revenue		47,651		90,348
Presented without adoption of ASC 606 | Europe | Tech-enabled
Revenue
Revenue		$ 13,415		$ 25,625