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Cash based compensation award, expenses

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Period Of Service From Grant Date Stock Options Awarded Not Subject To Forfeiture

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Provisional compensation cash award approved for future grant by compensation committee, units

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Provisional Compensation Cash Award Approved for Future Grant by Compensation Committee, Value

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Share Based Compensation Arrangement By Share Based Payment Award Aggregate Fair Value

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Share Based Compensation Arrangement By Share Based Payment Award Award Vesting Date

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Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Option Nonvested Intrinsic Value

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Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period Fair Value

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Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Value

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Ultimate Award Value Multiples of Original Value of Units, Maximum

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Ultimate Award Value Multiples of Original Value of Units, Minimum

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Amount of noncash expense for award of restricted stock or unit under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Date the equity-based award expires, in CCYY-MM-DD format.

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Number of shares authorized for issuance under share-based payment arrangement.

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Number of options outstanding, including both vested and non-vested options.

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Number of shares issued under share-based payment arrangement.

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Description of terms of award under share-based payment arrangement.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Restricted Stock, Performance Share and Cash Awards - Additional Information (Detail)			3 Months Ended						9 Months Ended
	Mar. 14, 2019 USD ($) shares	Mar. 15, 2018 USD ($) shares	Sep. 30, 2019 USD ($) shares	Mar. 31, 2019 shares	Sep. 30, 2018 USD ($) shares	Mar. 31, 2018 shares	Mar. 31, 2017 shares	Mar. 31, 2016	Sep. 30, 2019 USD ($) Times shares	Sep. 30, 2018 USD ($) shares	Dec. 31, 2018 shares	Mar. 16, 2017 USD ($) shares	Mar. 17, 2016 USD ($) shares
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Share-based compensation, shares outstanding \| shares			8,400,000						8,400,000		8,800,000
Shares granted in the period \| shares				399,900		420,200
Performance awards period, years									3 years
Long Term Incentive Plan [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Share-based compensation, shares outstanding, Value			$ 4,000,000.0						$ 4,000,000.0
Share-based compensation, shares outstanding \| shares			2,800,000						2,800,000
Shares granted in the period \| shares									2,800,000
Restricted Stock Units (RSUs) [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Shares granted in the period \| shares				399,900		420,200
Fair value of grants in period			$ 31,800,000		$ 28,700,000
Share based payment award vesting date				Mar. 14, 2024		Mar. 15, 2023
Restricted stock or unit expense			7,700,000		6,000,000.0				$ 22,500,000	$ 20,600,000
Unvested Restricted Stock [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Total intrinsic value			201,900,000		141,600,000				201,900,000	141,600,000
Equity awards with an aggregate fair value									2,000,000.0	22,400,000
Performance Shares [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Equity awards with an aggregate fair value									$ 5,700,000	$ 3,700,000
Shares authorized \| shares	73,600	78,200
Performance unit awards approved, Fair value	$ 5,800,000	$ 5,300,000
Provisional awards, terms									Granted units for the 2019 and 2018 provisional awards will fully vest based on continuous employment through March 14, 2022 and March 15, 2021, respectively, and will be settled in shares of our common stock on a one-for-one basis as soon as practicable thereafter.
Performance awards period, years									1 year
Vesting period, years									2 years
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period \| shares									0	0
2019 Provisional Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Performance awards expiration date									Jan. 01, 2022
Cash-based compensation awards, expenses			2,500,000						$ 6,600,000
2017 Performance Share Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Provisional awards, terms									The 2019 and 2018 awards are subject to a three-year performance period that begins on January 1, 2019 and 2018, respectively, and vest on the three-year anniversary of the date of grant (March 14, 2022 and March 15, 2021).
Vesting period, years									3 years
Performance awards expiration date									Mar. 14, 2022
2017 Provisional Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Performance awards expiration date									Jan. 01, 2020
Cash-based compensation awards, expenses			$ 2,700,000		2,400,000				$ 7,700,000	$ 6,300,000
2016 Provisional Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Performance awards expiration date							Jan. 01, 2019
Provisional compensation cash award approved for future grant by compensation committee, units \| shares			(341,000)						(341,000)
Cash-based compensation awards, expenses					$ 2,500,000				$ 22,400,000	$ 9,100,000
2015 Provisional Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Performance awards expiration date								Jan. 01, 2019
Provisional compensation cash award approved for future grant by compensation committee, units \| shares					(269,000)					(269,000)
Cash-based compensation awards, expenses										$ 15,800,000
Minimum [Member] \| Long Term Incentive Plan [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Period of service from grant date stock options awarded not subject to forfeiture									2 years	2 years
Minimum [Member] \| Restricted Stock Units (RSUs) [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Period of service from grant date stock options awarded not subject to forfeiture									2 years
Officer and Key Employees [Member] \| Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Provisional awards, terms									The ultimate award value will be equal to the trailing twelve-month price of our common stock on December 31, 2021, multiplied by the number of units subject to the award, but limited to between 0.5 and 1.5 times the original value of the units determined as of the grant date.
Performance awards period, years									1 year
Vesting period, years									3 years
Provisional compensation cash awards approved for future grant by compensation committee, value	$ 16,500,000	$ 15,000,000.0										$ 14,300,000
Provisional compensation cash award approved for future grant by compensation committee, units \| shares	206,800	219,000	190,000			242,000			190,000			255,000
Ultimate award value, multiples of original value of the units, minimum \| Times									0.005
Ultimate award value, multiples of original value of the units, maximum \| Times									0.015
Officer and Key Employees [Member] \| 2016 Provisional Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Provisional compensation cash awards approved for future grant by compensation committee, value													$ 17,400,000
Provisional compensation cash award approved for future grant by compensation committee, units \| shares							383,000						397,000
Executive Officer [Member] \| Minimum [Member] \| Long Term Incentive Plan [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Minimum age of employee with not subject to award forfeiture on condition compliance									55 years	55 years
Executive Officer [Member] \| Minimum [Member] \| Restricted Stock Units (RSUs) [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Minimum age of employee with not subject to award forfeiture on condition compliance				55 years		55 years