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Acquisitions - Additional Information (Detail)		3 Months Ended
Acquisitions - Additional Information (Detail)	Aug. 30, 2019 USD ($) Office Teammate	Dec. 31, 2019 USD ($)	Sep. 30, 2020 USD ($)
Business Acquisition [Line Items]
Goodwill		$ 415,149,000	$ 425,800,000
PCM [Member]
Business Acquisition [Line Items]
Cash purchase price	$ 745,562,000
Acquisition, percentage of issued and outstanding shares acquired	100.00%
Cash and cash equivalents acquired	$ 84,637,000
Number of office locations globally \| Office	40
Estimated fair value of net assets acquired	$ 407,031,000
Identifiable intangible assets	191,370,000
Goodwill	253,894,000
Tax deductible goodwill	0
PCM [Member] \| Customer Relationships
Business Acquisition [Line Items]
Goodwill balance due to adjustment in purchase price allocation		$ 56,700,000
Identifiable intangible assets	$ 178,900,000
PCM [Member] \| Trade Name [Member]
Business Acquisition [Line Items]
Useful Life	1 year
PCM [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Number of teammates \| Teammate	4,000
PCM [Member] \| Minimum [Member] \| Customer Relationships
Business Acquisition [Line Items]
Useful Life	10 years
PCM [Member] \| Minimum [Member] \| Non-compete Agreements [Member]
Business Acquisition [Line Items]
Useful Life	2 years
PCM [Member] \| Maximum [Member] \| Customer Relationships
Business Acquisition [Line Items]
Useful Life	12 years
PCM [Member] \| Maximum [Member] \| Non-compete Agreements [Member]
Business Acquisition [Line Items]
Useful Life	3 years