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Deferred Compensation - Additional information (Detail) - USD ($) shares in Millions | 3 Months Ended | 12 Months Ended
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Dec. 31, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Mar. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
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 made 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 | $ 11,500,000 |  | $ 14,000,000 |  | $ 10,100,000 |  |  |  |
Charge to compensation expenses related to awards |  |  |  |  |  |  | $ 9,100,000 | $ 9,600,000 | $ 7,500,000
Cash and equity awards with aggregate fair value vested and distributed to participants |  |  |  |  |  |  | 6,400,000 | 8,400,000 | 7,600,000
Unearned deferred compensation, value |  |  |  |  |  |  | $ 57,600,000 | $ 54,700,000 |
Unearned deferred compensation, shares |  |  |  |  |  |  | 2.7 | 2.6 |
Total intrinsic value of unvested equity based awards |  |  |  |  |  |  | $ 199,800,000 | $ 166,000,000 |
Deferred Cash Participation Plan (DCPP) [Member] |  |  |  |  |  |  |  |  |
Investments And Employee Deferred Compensation Plan [Line Items] |  |  |  |  |  |  |  |  |
Awards approved by committee, value |  | $ 5,600,000 |  | $ 5,100,000 |  | $ 3,100,000 |  |  |
Charge to compensation expenses related to awards |  |  |  |  |  |  | 3,000,000 | 2,500,000 | 1,500,000
Cash and equity awards with aggregate fair value vested and distributed to participants |  |  |  |  |  |  | 3,600,000 | 0 | 0
Deferred Equity Participation Plan Sub Plans [Member] |  |  |  |  |  |  |  |  |
Investments And Employee Deferred Compensation Plan [Line Items] |  |  |  |  |  |  |  |  |
Awards approved by committee, value |  |  |  |  |  |  | 900,000 | 4,000,000 | 13,600,000
Charge to compensation expenses related to awards |  |  |  |  |  |  | 2,200,000 | 1,900,000 | 1,300,000
Cash and equity awards with aggregate fair value vested and distributed to participants |  |  |  |  |  |  | $ 0 | $ 0 | $ 0

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- Definition Deferred equity participation sub plan distributions requisite service description. + References No definition available. + Details
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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + 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=109197908&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=109197908&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=109197908&loc=d3e5070-113901 + Details
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