Segment and geographic information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment region	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Revenues from External Customers and Long-Lived Assets [Line Items]
Number of operating segments | segment			1
Number of geographic regions company operates in | region			3
Total revenue	$ 341,009	$ 318,609	$ 652,906	$ 618,714
Property and equipment, net	249,834		249,834		$ 249,715
Outside The United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	222,000	$ 204,000	422,000	$ 393,000
Property and equipment, net	$ 133,000		$ 133,000		$ 132,000