Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Goodwill, Gross
Balance, beginning of period			$ 227,224
Purchase accounting adjustments			4,627
Foreign currency fluctuations			(7,542)
Balance, end of period	$ 224,309		224,309		$ 227,224
Accumulated Impairment Losses
Balance, beginning of period			(41,180)
Foreign currency fluctuations			1,490
Balance, end of period	(39,690)		(39,690)		(41,180)
Goodwill, Net
Balance, beginning of period			186,044
Purchase accounting adjustments			4,627
Foreign currency fluctuations			(6,052)
Balance, end of period	184,619		184,619		186,044
Acquired Finite-lived Intangible Assets
Original cost	192,839		192,839		195,912
Accumulated amortization	(39,865)		(39,865)		(23,565)
Carrying value	152,974		152,974		172,347
Purchase of Intangible Assets			2,607	$ 2,500
Amortization expense	5,720	$ 7,650	17,378	$ 11,430
Estimated aggregate amortization expense of Intangible Assets
Remaining 2018	5,456		5,456
2019	21,268		21,268
2020	19,827		19,827
2021	18,244		18,244
2022	15,965		15,965
Thereafter	72,214		72,214
Total	152,974		152,974
Customer Lists
Acquired Finite-lived Intangible Assets
Original cost	144,760		144,760		149,355
Accumulated amortization	(29,908)		(29,908)		(17,870)
Carrying value	114,852		$ 114,852		$ 131,485
Weighted-average original life (in years)			15 years		15 years
Trade Names
Acquired Finite-lived Intangible Assets
Original cost	30,945		$ 30,945		$ 31,968
Accumulated amortization	(4,631)		(4,631)		(2,436)
Carrying value	26,314		$ 26,314		$ 29,532
Weighted-average original life (in years)			10 years		10 years
Technology
Acquired Finite-lived Intangible Assets
Original cost	17,134		$ 17,134		$ 14,589
Accumulated amortization	(5,326)		(5,326)		(3,259)
Carrying value	$ 11,808		$ 11,808		$ 11,330
Weighted-average original life (in years)			11 years		11 years
Purchase of Intangible Assets			$ 2,500