Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Payables and Accruals [Abstract]
Payroll and other employee related costs	$ 13,345	$ 13,887
Professional services and consulting and other vendor fees	11,494	14,559
Unrecognized tax benefits	4,772	4,240
Sales commissions	1,876	3,312
Restructuring Reserve	2,526	2,551	$ 1,328
Contingent earnout (see Note 8)	0	210
Other	3,194	1,491
Total	$ 37,207	$ 40,250