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Summary of Significant Accounting Policies - Acquisitions (Detail) - item	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Number of business acquired	4	18	32

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- References

No definition available.

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- Definition

The number of businesses acquired by the entity during the period.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
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