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Supplemental Disclosures of Cash Flow Information - Additional Information (Detail) - Qualified Contributory Savings and Thrift 401(k) Plan [Member] - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Matching contributions by employer, percentage	100.00%
Percentage of eligible compensation for matching contributions by employer	5.00%
Matching contributions vesting schedule	5 years
Contribution expense to plan	$ 45.9	$ 43.8

X

- Definition

Defined benefit plan percentage of eligible compensation for matching contributions by employer.

+ References

No definition available.

+ Details

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Period Type:	duration

X

- Definition

Matching contributions vesting schedule.

+ References

No definition available.

+ Details

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X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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X

- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

+ Details

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Balance Type:	debit
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X

- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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X

- Details

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Namespace Prefix:
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