Business Segments - Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenue from third parties									$ 1,136,256	$ 1,090,704	$ 1,029,353
Revenue from other segments									0	0	0
Total revenue	$ 300,950	$ 288,386	$ 279,530	$ 267,390	$ 270,418	$ 279,993	$ 269,220	$ 271,073	1,136,256	1,090,704	1,029,353
Adjusted EBITDA									62,275	59,153	50,799
Total assets	$ 640,019				$ 590,999				640,019	590,999
North America
Segment Reporting Information [Line Items]
Revenue from third parties									776,400	734,164	708,532
Revenue from other segments									5,469	6,029	7
Total revenue									781,869	740,193	708,539
Adjusted EBITDA									78,079	67,969	63,744
International
Segment Reporting Information [Line Items]
Revenue from third parties									359,856	356,540	320,821
Revenue from other segments									15,137	17,526	8,691
Total revenue									374,993	374,066	329,512
Adjusted EBITDA									20,063	22,576	14,936
Other (2)
Segment Reporting Information [Line Items]
Revenue from third parties									0	0	0
Revenue from other segments									(20,606)	(23,555)	(8,698)
Total revenue									(20,606)	(23,555)	(8,698)
Adjusted EBITDA									$ (35,867)	$ (31,392)	$ (27,881)