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Employee Deferred Compensation Plan and Employee Stock Purchase Plan - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands | 1 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2001 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Nov. 05, 2018 | Jun. 06, 2018
Employee Stock Ownership Plan E S O P Disclosures [Line Items] |  |  |  |  |  |
Percentage contribution, compensation |  | 100.00% |  |  |  |
Matching percentage, employee contribution |  | 5.00% |  |  |  |
Company's contributions amount |  | $ 2,172 | $ 1,997 | $ 1,914 |  |
Common stock under employee stock purchase plan, par value |  | $ 10 | $ 10 |  | $ 0.10 |
Shares of common stock purchased through the plan |  | 49,668 | 47,229 | 35,950 |  |
Employee Stock Purchase Plan |  |  |  |  |  |
Employee Stock Ownership Plan E S O P Disclosures [Line Items] |  |  |  |  |  |
Number of common stock shares under employee stock purchase plan | 1,000,000 |  |  |  |  |
Common stock under employee stock purchase plan, par value | $ 0.10 |  |  |  |  |
Employee stock purchase plan offering period |  | January 1 and July 1 of each year |  |  |  |
Employee stock purchase plan expiration date |  | Dec. 31, 2028 |  |  |  |
Commons stock plan available for sale under plan |  |  |  |  |  | 995,000
Available common stock under plan |  | 593,962 | 643,630 | 690,859 |  |

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- Definition Employee stock purchase plan purchase price offering period description. + References No definition available. + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + 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 -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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