Commitments and contingencies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 CNY (¥)	Dec. 31, 2016 EUR (€)	Dec. 31, 2016 USD ($)	Sep. 30, 2015 EUR (€)	Sep. 30, 2015 USD ($)	May 31, 2015 CNY (¥)	May 31, 2015 USD ($)	Oct. 31, 2014 CNY (¥)
Revolving Credit Facility | Line of Credit | BPI France Revolving Credit Facility
Loss Contingencies [Line Items]
Long-term line of credit					€ 100,000	$ 100,000
Maximum borrowing capacity					1,000,000.0	1,100,000.0
Revolving Credit Facility | Line of Credit | HSBC Revolving Loan Facility
Loss Contingencies [Line Items]
Long-term line of credit				¥ 30,000,000		4,300,000
Maximum borrowing capacity				¥ 40,000,000.0		5,800,000.0			¥ 40,000,000.0	$ 5,800,000.0	¥ 15,000,000
Revolving Credit Facility | Line of Credit | Bank Syndicate RCF
Loss Contingencies [Line Items]
Long-term line of credit						75,000,000
Maximum borrowing capacity					250,000,000.0	263,500,000.0	€ 250,000,000	$ 263,500,000.0
Line of Credit and Overdraft Facility | HSBC and LCL Facilities | Line of Credit
Loss Contingencies [Line Items]
Maximum borrowing capacity					€ 9,400,000.0	$ 9,900,000.0
Property Leases
Loss Contingencies [Line Items]
Operating lease expense	$ 32,100,000	$ 23,600,000	$ 18,800,000
Hosting Services
Loss Contingencies [Line Items]
Operating lease expense	$ 42,000,000	$ 30,400,000	$ 24,800,000