Fair Value of Financial Instruments - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Apr. 01, 2015	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Revenue target	$ 80,000
Contingent obligation due selling unitholders of Cogent		$ 17,354		$ 17,354		$ 13,763
Increase (decrease) in fair value contingent consideration				3,591	$ (7,513)
Cogent Partners, LP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maximum contingent consideration	$ 18,900
Conditional consideration (shares)	334,048
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
Contingent obligation due selling unitholders of Cogent	$ 13,100	17,400		17,400
Increase (decrease) in fair value contingent consideration		$ 2,700	$ (1,500)	$ 3,600	$ (7,500)