Fair Value Measurements and Investments - Schedule of Reconciliation For Contingent Consideration Measured At Fair Value Using Significant Unobservable Inputs (Level 3) (Detail) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Contingent consideration at January 1	$ 28,560
Acquisition date fair value		$ 25,491
Increase in fair value recognized in acquisition-related amortization and remeasurement	28,140	2,689
Payment made	(15,000)
Contingent consideration at September 30	$ 41,700	$ 28,180