Accrued expenses and other current liabilities Accrued expenses and other current liabilities - Summary of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accounts Payable and Accrued Liabilities, Current [Abstract]
Accrued expenses	$ 30,690	$ 26,238
Derivative instruments	1,430	1,226
Client liability account	4,005	2,217
Other current liabilities	7,139	4,569
Accrued expenses and other current liabilities	$ 43,264	$ 34,250