Fair Value of Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements, Recurring and Nonrecurring

Liabilities Measured at Fair Value on a Recurring Basis as of September 30, 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 September 30, 2018
	(in thousands, unaudited)
Liabilities
Contingent obligation due selling unitholders of Cogent	$	—	$	17,784	$	—	$	17,784
Total	$	—	$	17,784	$	—	$	17,784

Liabilities Measured at Fair Value on a Recurring Basis as of December 31, 2017

	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, 2017
	(in thousands)
Liabilities
Contingent obligation due selling unitholders of Cogent	$	—	$	—	$	13,763	$	13,763
Total	$	—	$	—	$	13,763	$	13,763

Assets Measured at Fair Value on a Recurring Basis as of September 30, 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 September 30, 2018
	(in thousands, unaudited)
Assets
Cash and cash equivalents	$	46,224	$	—	$	—	$	46,224
Total	$	46,224	$	—	$	—	$	46,224

Assets Measured at Fair Value on a Recurring Basis as of December 31, 2017

	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, 2017
	(in thousands)
Assets
Cash and cash equivalents	$	193,315	$	—	$	—	$	193,315
Total	$	193,315	$	—	$	—	$	193,315

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 and nine month periods ended September 30, 2018 are as follows:

	Opening Balance as of July 1, 2018		Total realized and unrealized gains (losses) included in Net Income			Unrealized gains (losses) included in Other Comprehen-sive Income		Purchases		Issues		Sales		Transfers Out			Closing Balance as of September 30, 2018		Unrealized gains (losses) for Level 3 liabilities outstanding at September 30, 2018
	(in thousands, unaudited)
Liabilities
Contingent obligation due selling unitholders of Cogent	$	17,354	$	(430	)	$	—	$	—	$	—	$	—	$	(17,784	)	$	—	$	—
Total	$	17,354	$	(430	)	$	—	$	—	$	—	$	—	$	(17,784	)	$	—	$	—

	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		Transfers Out			Closing Balance as of September 30, 2018		Unrealized gains (losses) for Level 3 liabilities outstanding at September 30, 2018
	(in thousands, unaudited)
Liabilities
Contingent obligation due selling unitholders of Cogent	$	13,763	$	(4,021	)	$	—	$	—	$	—	$	—	$	(17,784	)	$	—	$	—
Total	$	13,763	$	(4,021	)	$	—	$	—	$	—	$	—	$	(17,784	)	$	—	$	—

Changes in Level 3 liabilities measured at fair value on a recurring basis for the three and nine month periods ended September 30, 2017 are as follows:

	Opening Balance as of July 1, 2017		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 September 30, 2017		Unrealized gains (losses) for Level 3 liabilities outstanding at September 30, 2017
	(in thousands, unaudited)
Liabilities
Contingent obligation due to selling unitholders of Cogent	$	7,582	$	(1,874	)	$	—	$	—	$	—	$	—	$	—	$	9,456	$	(1,874	)
Total	$	7,582	$	(1,874	)	$	—	$	—	$	—	$	—	$	—	$	9,456	$	(1,874	)

	Opening Balance as of January 1, 2017		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 September 30, 2017		Unrealized gains (losses) for Level 3 liabilities outstanding at September 30, 2017
	(in thousands, unaudited)
Liabilities
Contingent obligation due to selling unitholders of Cogent	$	15,095	$	5,639	$	—	$	—	$	—	$	—	$	—	$	9,456	$	5,639
Total	$	15,095	$	5,639	$	—	$	—	$	—	$	—	$	—	$	9,456	$	5,639