Fair Value of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurements, Recurring and Nonrecurring

Liabilities Measured at Fair Value on a Recurring Basis as of March 31, 2019

	Quoted Prices in Active  Markets for Identical Assets (Level 1)		Significant Other Observable  Inputs (Level 2)		Significant Unobservable  Inputs (Level 3)		Balance as of March 31, 2019
	(in thousands, unaudited)
Liabilities
Contingent obligation due selling unitholders of Cogent	$	—	$	18,868	$	—	$	18,868
Total	$	—	$	18,868	$	—	$	18,868

Liabilities Measured at Fair Value on a Recurring Basis as of December 31, 2018

	Quoted Prices in Active  Markets for Identical Assets (Level 1)		Significant Other Observable  Inputs (Level 2)		Significant Unobservable  Inputs (Level 3)		Balance as of December 31, 2018
	(in thousands)
Liabilities
Contingent obligation due selling unitholders of Cogent	$	—	$	18,293	$	—	$	18,293
Total	$	—	$	18,293	$	—	$	18,293

Assets Measured at Fair Value on a Recurring Basis as of March 31, 2019

	Quoted Prices in Active  Markets for Identical Assets (Level 1)		Significant Other Observable  Inputs (Level 2)		Significant Unobservable  Inputs (Level 3)		Balance as of March 31, 2019
	(in thousands, unaudited)
Assets
Cash equivalents	$	25,052	$	—	$	—	$	25,052
Total	$	25,052	$	—	$	—	$	25,052

Assets Measured at Fair Value on a Recurring Basis as of December 31, 2018

	Quoted Prices in Active  Markets for Identical Assets (Level 1)		Significant Other Observable  Inputs (Level 2)		Significant Unobservable  Inputs (Level 3)		Balance as of December 31, 2018
	(in thousands)
Assets
Cash equivalents	$	72,193	$	—	$	—	$	72,193
Total	$	72,193	$	—	$	—	$	72,193

Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation

Changes in Level 3 liabilities measured at fair value on a recurring basis for the three month period ended March 31, 2018 are as follows:

	Opening Balance as of January 1, 2018		Total realized and unrealized gains (losses) included in Net Income			Unrealized gains (losses) included in Other Comprehen-sive Income		Purchases		Issues		Sales		Settlements		Closing Balance as of March 31, 2018		Unrealized gains (losses) for Level 3 liabilities outstanding at March 31, 2018
	(in thousands, unaudited)
Liabilities
Contingent obligation due to selling unitholders of Cogent	$	13,763	$	(910	)	$	—	$	—	$	—	$	—	$	—	$	14,673	$	(910	)
Total	$	13,763	$	(910	)	$	—	$	—	$	—	$	—	$	—	$	14,673	$	(910	)