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Computations of Basic and Diluted Earnings Per Share (Parenthetical) (Detail) - shares | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Earnings Per Share Disclosure [Line Items] |  |  |  |  |
Weighted average shares of participating unvested restricted stock | 815,000 | 721,000 |  | 640,000 |
Restricted Stock Units (RSUs) |  |  |  |  |
Earnings Per Share Disclosure [Line Items] |  |  |  |  |
Common equivalent shares for restricted stock units | 682,000 | 300,000 | [1] | 288,000 | [1]
[1] | For the year ended December 31, 2020, approximately 682 common equivalent shares for restricted stock units were excluded because they were anti-dilutive.

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- Definition This element represents nonvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid). Basic and dilutive earnings per share are generally disclosed for such shares using the two-class method. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 68B -URI http://asc.fasb.org/extlink&oid=121326447&loc=SL5498026-109256 + Details
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- Definition Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 22 -URI http://asc.fasb.org/extlink&oid=121326447&loc=d3e1707-109256 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 28A -URI http://asc.fasb.org/extlink&oid=121326447&loc=d3e1500-109256 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 23 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121326447&loc=d3e1757-109256 + Details
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