Acquisitions - Schedule of Fair Values of Identifiable Assets and Liabilities of Acquisitions (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021	Dec. 31, 2020
Liabilities
Goodwill arising from acquisitions	$ 2,247,466		$ 2,206,004	$ 2,163,339
2021 Acquisitions
Consideration:
Cash		$ 20,426
Holdbacks		1,442
Fair value of contingent consideration		5,116
Purchase price		26,984
Identifiable intangible assets		11,083
Assets
Accounts receivable		3,382
Property and equipment		86
Identifiable intangible assets		11,083
Total assets		14,551
Liabilities
Total liabilities		4,222
Total identifiable net assets		8,525
Redeemable noncontrolling interest		1,804
Goodwill arising from acquisitions		$ 18,459
2021 Acquisitions | Client relationships [Member]
Consideration:
Weighted Average Useful Life		7 years
Identifiable intangible assets		$ 10,082
Assets
Identifiable intangible assets		$ 10,082
2021 Acquisitions | Trade names [Member]
Consideration:
Weighted Average Useful Life		10 years
Identifiable intangible assets		$ 1,001
Assets
Identifiable intangible assets		$ 1,001
2022 Acquisitions
Consideration:
Cash	67,611
Holdbacks	810
Fair value of contingent consideration	510
Purchase price	68,931
Identifiable intangible assets	21,220
Assets
Accounts receivable	6,190
Other assets	2,815
Identifiable intangible assets	21,220
Total assets	30,225
Liabilities
Accounts payable	5,266
Deferred tax liabilities and other	6,601
Total liabilities	11,867
Total identifiable net assets	18,358
Goodwill arising from acquisitions	$ 50,573
2022 Acquisitions | Client relationships [Member]
Consideration:
Weighted Average Useful Life	6 years
Identifiable intangible assets	$ 21,220
Assets
Identifiable intangible assets	$ 21,220