Fair value measurement - financial assets and liabilities carried at fair value measured on recurring basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments in marketable securities	$ 8,671	$ 9,045
Derivative assets	16,050	1,221
Derivative liabilities	8,581	1,426
Contingent consideration liabilities	304,248	272,136
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments in marketable securities	8,671	9,045
Derivative assets	0	0
Derivative liabilities	0	0
Contingent consideration liabilities	0	0
Significant Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments in marketable securities	0	0
Derivative assets	16,050	1,221
Derivative liabilities	8,581	1,426
Contingent consideration liabilities	0	0
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments in marketable securities	0	0
Derivative assets	0	0
Derivative liabilities	0	0
Contingent consideration liabilities	$ 304,248	$ 272,136