Fair Value of Financial Instruments - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended
	Apr. 01, 2015	Mar. 31, 2018	Mar. 31, 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		$ 14,673		$ 13,763
Increase (decrease) in fair value contingent consideration		910	$ (6,005)
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	14,700
Increase (decrease) in fair value contingent consideration		$ 900	$ (6,000)