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Deferred Compensation - Additional Information (Detail) - USD ($) shares in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2021 | Mar. 31, 2021 | Sep. 30, 2020 | Mar. 31, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
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 if later. |  |
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 the earlier of fifteen years or the participant reaching age 65. |  |
Deferred Equity Participation Sub-plans, distributions to key executives, age |  |  |  |  | age 65 |  |
Deferred Equity Participation Plan (DEPP) [Member] |  |  |  |  |  |  |
Investments And Employee Deferred Compensation Plan [Line Items] |  |  |  |  |  |  |
Awards approved by committee, value |  | $ 17,000,000.0 |  | $ 14,100,000 |  |  |
Charge to compensation expenses related to awards | $ 3,800,000 |  | $ 3,000,000.0 |  | $ 10,300,000 | $ 9,000,000.0 |
Unearned deferred compensation, value |  |  |  |  | $ 74,300,000 |  | $ 60,500,000
Unearned deferred compensation, shares |  |  |  |  | 2.7 |  | 2.6
Total intrinsic value of unvested equity based awards |  |  |  |  | $ 402,800,000 |  | $ 327,800,000
Cash and equity awards with aggregate fair value vested and distributed to participants |  |  |  |  | 10,100,000 | 9,800,000 |
Deferred Equity Participation Plan Sub Plans [Member] |  |  |  |  |  |  |
Investments And Employee Deferred Compensation Plan [Line Items] |  |  |  |  |  |  |
Awards approved by committee, value |  | 3,200,000 |  | 1,800,000 |  |  |
Charge to compensation expenses related to awards | 500,000 |  | 700,000 |  | 1,900,000 | 2,100,000 |
Distributions from the sub-plans |  |  |  |  | 0 | 0 |
Deferred Cash Participation Plan (DCPP) [Member] |  |  |  |  |  |  |
Investments And Employee Deferred Compensation Plan [Line Items] |  |  |  |  |  |  |
Awards approved by committee, value |  | $ 7,200,000 |  | $ 3,000,000.0 |  |  |
Charge to compensation expenses related to awards | $ 2,900,000 |  | $ 1,600,000 |  | 7,000,000.0 | 5,000,000.0 |
Cash and equity awards with aggregate fair value vested and distributed to participants |  |  |  |  | $ 6,700,000 | $ 7,300,000 |

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