Business Combinations - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Business	Sep. 30, 2019 USD ($) Business
Business Acquisition [Line Items]
Number of businesses acquired | Business			5	4
Percentage of voting equity interests acquired		100.00%		100.00%
Goodwill acquired expected to be tax deductible	$ 11,300		$ 11,300
Amortization of intangibles	6,974	$ 6,156	20,378	$ 18,065
Income tax expense (benefit)	9,773	7,610	24,578	17,135
Administrative [Member]
Business Acquisition [Line Items]
Acquisition-related costs	800	300	2,000	1,300
Combined Business Acquisitions [Member]
Business Acquisition [Line Items]
Amortization of intangibles	300	1,400	1,800	4,800
Income tax expense (benefit)	$ 38	$ 500	$ 100	$ 1,300