v3.8.0.1
Commitments and contingencies - Capital leases and notes payable and letters of credit (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Fair value    
Current portion of capital leases and notes payable $ 5,771 $ 3,993
Long-term portion of capital leases and notes payable $ 6,747 $ 4,612
Letters of Credit    
Commitments and contingencies    
Term period of Letters of Credit agreements 1 year  
Letters of credit    
Current issued borrowing capacity $ 8,204  
Outstanding balance $ 0