Goodwill and Intangible Assets - Goodwill activity (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Goodwill, Roll forward
Goodwill, gross, at the beginning of the year		$ 377,302
Accumulated impairment losses		(24,291)
Goodwill, net, at the beginning of the year	$ 353,011
Business combinations	40
Foreign currency translation adjustment	1,403
Goodwill, net, at the end of the year	354,454
North America
Goodwill, Roll forward
Goodwill, gross, at the beginning of the year		240,837
Goodwill, net, at the beginning of the year	240,837
Foreign currency translation adjustment	1,280
Goodwill, net, at the end of the year	242,117
Europe
Goodwill, Roll forward
Goodwill, gross, at the beginning of the year		136,465
Accumulated impairment losses		$ (24,291)
Goodwill, net, at the beginning of the year	112,174
Business combinations	40
Foreign currency translation adjustment	123
Goodwill, net, at the end of the year	$ 112,337