Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - Level 3 [Member] - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Undiscounted value of the payments on all contingencies	$ 84,700	$ 85,200
Accounts Payable, Accrued and Other Liabilities [Member] | Contingent Consideration [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration, Fair Value	61,076	$ 67,172
Other Assets [Member] | Non-recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities, Assets	$ 49,100