Fair Value Measurements - Schedule of Financial Assets and Liabilities Recorded at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Inputs, Level 3 [Member] | Debt Security [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value	$ 17,820	$ 16,050	$ 12,220
Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value	18,529	16,706
Contingent consideration	(28,560)
Deferred compensation plan, Liabilities	(1,275)	(1,379)
Liabilities fair value, Total	(29,835)	(1,379)
Fair Value, Measurements, Recurring [Member] | Treasury Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value	490	556
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value	219
Fair Value, Measurements, Recurring [Member] | Debt Security [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value	17,820	16,050
Fair Value, Measurements, Recurring [Member] | Collective Trust Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value		100
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value	490	556
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Treasury Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value	490	556
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value	219	100
Deferred compensation plan, Liabilities	(1,275)	(1,379)
Liabilities fair value, Total	(1,275)	(1,379)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value	219
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Collective Trust Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value		100
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value	17,820	16,050
Contingent consideration	(28,560)
Liabilities fair value, Total	(28,560)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Security [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets fair value	$ 17,820	$ 16,050