Fair Value of Financial Instruments - Narrative (Details) $ in Thousands		12 Months Ended
	Apr. 01, 2015 USD ($) shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Revenue target	$ 80,000
Distribution period ending on the second anniversary of the closing (years)	2 years
Distribution period ending on the fourth anniversary of the closing (years)	2 years
Distribution period ending On March 31 2017 (years)	2 years
Distribution period ending On March 31 2019 (years)	2 years
Contingent obligation due selling unitholders of Cogent		$ 18,293	$ 13,763
Increase (decrease) in fair value of contingent obligation		4,531	(1,332)	$ 1,448
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent obligation due selling unitholders of Cogent		18,293	13,763
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent obligation due selling unitholders of Cogent		$ 18,293	0
Discount rate		0.132
Cogent Partners, LP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration, cash	$ 18,900
Possible contingent consideration (shares) | shares	334,048
Contingent obligation due selling unitholders of Cogent	$ 13,100
Increase (decrease) in fair value of contingent obligation		$ 4,500	$ (1,300)	$ 1,500