Liabilities Measured at Fair Value Using Level 3 Inputs (Detail) - Contingent Payment $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent consideration, Beginning balance	$ 132,834
Changes in the fair value of other contingent consideration	20,612
Realized foreign exchange gain on settlement of contingent consideration	(1,928)
Foreign exchange remeasurement of Euro denominated contingent   acquisition consideration	(1,266)
Contingent consideration, Ending balance	50,793
Merck Serono
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Milestone payments	(83,472)
Lead Therapeutics, Inc
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Milestone payments	$ (15,987)