Revenue - Disaggregated revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenue	$ 52,642	$ 47,406
Owned Regions
Disaggregation of Revenue [Line Items]
Total revenue	31,363	28,552
Independent Regions
Disaggregation of Revenue [Line Items]
Total revenue	11,149	10,750
Global and Other
Disaggregation of Revenue [Line Items]
Total revenue	10,130	8,104
U.S.
Disaggregation of Revenue [Line Items]
Total revenue	36,749	34,078
Canada
Disaggregation of Revenue [Line Items]
Total revenue	5,763	5,224
Global and Other
Disaggregation of Revenue [Line Items]
Total revenue	$ 10,130	$ 8,104