Business Segments - Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		9 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	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenue from third parties													$ 1,138,361	$ 1,094,402	$ 1,028,892
Revenue from other segments													0	0	0
Total revenue	$ 305,367	$ 288,523	$ 280,066	$ 264,405	$ 275,727	$ 276,002	$ 272,212	$ 270,461	$ 544,471	$ 542,673	$ 832,994	$ 818,675	1,138,361	1,094,402	1,028,892
Adjusted EBITDA													57,883	58,612	50,679
Total assets	$ 649,638	$ 660,532	$ 616,620	$ 600,086	$ 593,987	$ 613,393	$ 597,148	$ 599,321	$ 616,620	$ 597,148	$ 660,532	$ 613,393	649,638	593,987
North America
Segment Reporting Information [Line Items]
Revenue from third parties													780,511	736,140	708,071
Revenue from other segments													5,469	6,029	7
Total revenue													785,980	742,169	708,078
Adjusted EBITDA													74,230	68,434	63,436
International
Segment Reporting Information [Line Items]
Revenue from third parties													357,850	358,262	320,821
Revenue from other segments													15,137	17,526	8,691
Total revenue													372,987	375,788	329,512
Adjusted EBITDA													19,520	21,570	15,124
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)