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Deferred Compensation - Additional information (Detail) - USD ($) shares in Millions, $ in Millions | 3 Months Ended | 12 Months Ended
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Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Investments And Employee Deferred Compensation Plan [Line Items] |  |  |  |  |  |  |  |
Deferred Equity Participation Plan, distributions to key executives, age |  |  |  |  |  | age 62 (or the one-year anniversary of the date of the grant for participants over the age of 61 as of the grant date) or upon or after their actual retirement. |  |
Deferred Equity Participation Sub-plans, distributions to key executives, age |  |  |  |  |  | age 65 |  |
Deferred Equity Participation Sub-plans, distributions requisite service description |  |  |  |  |  | we annually make awards under sub-plans of the DEPP for certain production staff, which generally provide for vesting and/or distributions no sooner than five years from the date of awards, although certain awards vest and/or distribute after earlier of fifteen years or the participant reaching age 65. |  |
Deferred Equity Participation Plan (DEPP) [Member] |  |  |  |  |  |  |  |
Investments And Employee Deferred Compensation Plan [Line Items] |  |  |  |  |  |  |  |
Awards approved by committee, value |  |  | $ 10.1 | $ 11.5 | $ 14.0 |  |  |
Charge to compensation expenses related to awards |  |  |  |  |  | $ 9.8 | $ 9.1 | $ 9.6
Cash and equity awards with aggregate fair value vested and distributed to participants |  |  |  |  |  | 3.1 | 6.4 | 8.4
Unearned deferred compensation, value |  |  |  |  |  | $ 64.5 | $ 57.6 |
Unearned deferred compensation, shares |  |  |  |  |  | 2.9 | 2.7 |
Total intrinsic value of unvested equity based awards |  |  |  |  |  | $ 276.3 | $ 199.8 |
Deferred Cash Participation Plan (DCPP) [Member] |  |  |  |  |  |  |  |
Investments And Employee Deferred Compensation Plan [Line Items] |  |  |  |  |  |  |  |
Awards approved by committee, value | $ 1.6 | $ 7.7 | $ 2.4 | $ 5.6 | $ 5.1 |  |  |
Charge to compensation expenses related to awards |  |  |  |  |  | 5.2 | 3.0 | 2.5
Cash and equity awards with aggregate fair value vested and distributed to participants |  |  |  |  |  | 2.5 | 3.6 |
Deferred Equity Participation Plan Sub Plans [Member] |  |  |  |  |  |  |  |
Investments And Employee Deferred Compensation Plan [Line Items] |  |  |  |  |  |  |  |
Awards approved by committee, value |  |  |  |  |  | 2.6 | 0.9 | 4.0
Charge to compensation expenses related to awards |  |  |  |  |  | 2.4 | 2.2 | 1.9
Distributions from the sub-plans |  |  |  |  |  | $ 0.5 | $ 0.0 | $ 0.0

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- Definition Deferred Equity Participation Plan, Distributions to Key Executives, Age + References No definition available. + Details
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- Definition Deferred equity participation sub plan distributions requisite service description. + References No definition available. + Details
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- Definition Deferred equity participation sub plan distributions to key executives age. + References No definition available. + Details
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- Definition Investments And Employee Deferred Compensation Plan [Line Items] + References No definition available. + Details
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- Definition Amount of expense for award under share-based payment arrangement. Excludes amount capitalized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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