Summary of Changes in Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Contingent Consideration [Member]
Fair Value, Net Derivative Asset (Liability) and Contingent Consideration Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at December 31, 2018	$ 25,845
Additions	5,008
Fair value adjustments	6
Balance at March 31, 2019	30,859
1.25% Cash Convertible Senior Notes [Member]
Fair Value, Net Derivative Asset (Liability) and Contingent Consideration Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at December 31, 2018	(870)
Additions	0
Fair value adjustments	375
Balance at March 31, 2019	$ (495)