Fair Value of Financial Instruments - Quantitative Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Contingent obligation due selling unitholders of Cogent	$ 9,456	$ 15,095
Fair Value, Measurements, Recurring
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Contingent obligation due selling unitholders of Cogent	9,456	15,095
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Contingent obligation due selling unitholders of Cogent	9,456	$ 15,095
Fair Value, Measurements, Recurring | Contingent Consideration Liability | Present value of expected payments | Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Contingent obligation due selling unitholders of Cogent	$ 9,456
Fair Value, Measurements, Recurring | Contingent Consideration Liability | Present value of expected payments | Significant Unobservable Inputs (Level 3) | Weighted Average
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Discount Rate	13.00%