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Share-Based Compensation - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Shares issuable upon exercise of outstanding options | 1,227,074 | 2,437,609 | 2,818,433 |  | 2,868,053
Estimated pretax compensation expense | $ 20.0 |  |  |  |
Expiration period in years | 4 years |  |  |  |
Service period in years | 4 years |  |  |  |
Restricted stock units settled in shares exercisable in percentage | 25.00% |  |  |  |
Restricted stock units settled in cash exercisable in percentage | 25.00% |  |  |  |
Stock compensation and recognized liability | $ 0.2 | $ (2.3) | $ (2.2) |  |
Non-Employee Directors' Stock Options [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Expiration period in years | 10 years |  |  |  |
Employee stock options exercisable in percentage | 100.00% |  |  |  |
Employee Stock Option [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Expiration period in years | 10 years |  |  |  |
Service period in years | 4 years |  |  |  |
Employee Stock Option [Member] | Share-based Compensation Award, Tranche One [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Stock awards settled in stock exercisable in percentage | 25.00% |  |  |  |
Restricted Stock Units [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Number of shares to reduce shares available to grant by upon vesting of restricted stock awards and units | 2,146,050 | 1,921,192 | 2,017,477 | [1] | 1,453,823
Service period in years | 4 years |  |  |  |
Performance-based Restricted Stock Units [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Service period in years | 3 years |  |  |  |
2016 Incentive Compensation Plan [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Common stock subject to awards of stock options or stock appreciation rights payable in shares | 1.0 |  |  |  |
Common stock subject to any other form of award | 1.35 |  |  |  |
Common stock available for future share-based awards | 1,300,000 |  |  |  |
Shares issuable upon exercise of outstanding options | 600,000 |  |  |  |
Number of shares to reduce shares available to grant by upon vesting of restricted stock awards and units | 2,900,000 |  |  |  |
2008 Incentive Compensation Plan [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Shares issuable upon exercise of outstanding options | 600,000 |  |  |  |
Number of shares to reduce shares available to grant by upon vesting of restricted stock awards and units | 100,000 |  |  |  |
[1] | The weighted average grant-date fair value per unit as of December 31, 2018 reflects an adjusted fair value per unit from $10.59 to $12.70 due to the modification of grants approved by the Board of Directors during 2019 for our performance-based awards granted on December 14, 2018.

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- Definition Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (a)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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