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Stock-Based Compensation Plans (Additional Information) (Details) - USD ($) |  | 12 Months Ended
--- | --- | ---
May 01, 2012 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Cash used to settle stock based compensation transactions |  | $ 374,000 | $ 455,000 | $ 848,000
Cash received from exercise of stock options |  | $ 33,000 | $ 95,000 | $ 218,000
Performance period |  |  |  | 5 years 3 months 18 days
Percentage of total compensation |  | 4.00% |  |
Granted |  | 0 | 0 |
Stock Option and Incentive Plan 2003 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Maximum number of shares of stock reserved and available for issuance | 1,200,000 |  |  |
Stock Option and Incentive Plan 2012 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Stock based compensation, option granted, contractual life |  | 10 years |  |
Stock based compensation, vesting period |  | 5 years |  |
Stock Options [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Grant date fair value of share based awards |  |  |  | $ 8,000
Share-based compensation |  | $ 4,000 | $ 7,000 | 10,000
Tax benefit from share based compensation |  | 7,000 | 8,000 | 50,000
Unrecognized compensation cost for nonvested stock options |  | $ 3,000 |  |
Unrecognized compensation cost, recognition period |  | 2 years |  |
Total intrinsic value of options exercised |  | $ 90,000 | 309,000 | 395,000
Stock Options [Member] | SBM Financial, Inc. [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Tax benefit from share based compensation |  | 1,000 | 1,000 | 0
Restricted Stock Units (RSUs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Grant date fair value of share based awards |  | 500,000 | 657,000 | 887,000
Share-based compensation |  | 475,000 | 389,000 | 263,000
Tax benefit from share based compensation |  | 102,000 | 84,000 | 57,000
Unrecognized compensation cost related to nonvested shares |  | $ 1,196,000 |  |
Granted |  | 16,181 |  |
Restricted Stock [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Grant date fair value of share based awards |  | $ 1,000,000.0 | 724,000 | 753,000
Share-based compensation |  | 781,000 | 751,000 | 916,000
Tax benefit from share based compensation |  | 168,000 | 161,000 | 197,000
Unrecognized compensation cost related to nonvested shares |  | $ 646,000 |  |
Granted |  | 31,983 |  |
Management Stock Purchase Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Grant date fair value of share based awards |  | $ 83,000 | 85,000 | 139,000
Share-based compensation |  | 71,000 | 95,000 | 104,000
Tax benefit from share based compensation |  | 15,000 | 20,000 | 22,000
Cash received from issuance of share based awards |  | 247,000 | 250,000 | 232,000
Unrecognized compensation cost related to nonvested shares |  | $ 51,000 |  |
Granted |  | 11,210 |  |
Management Stock Purchase Plan [Member] | Interest and Other Liabilities [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Cash received from issuance of share based awards |  | $ 455,000 | 472,000 |
Long-Term Performance Share Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Share-based compensation |  | 332,000 | 532,000 | 291,000
Tax benefit from share based compensation |  | 71,000 | 114,000 | 63,000
Total intrinsic value of options exercised |  | $ 978,000 | 624,000 | 663,000
Performance period |  | 3 years |  |
Unrecognized compensation cost related to nonvested shares |  | $ 388,000 |  |
Granted |  | 28,766 |  |
Deferred Stock Awards [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Grant date fair value of share based awards |  | $ 169,000 | 153,000 | 155,000
Share-based compensation |  | 122,000 | 110,000 | 106,000
Tax benefit from share based compensation |  | $ 26,000 | $ 24,000 | $ 23,000
Percentage of total compensation |  | 10.00% |  |
Percentage vested on 65th birthday |  | 100.00% |  |
Qualified Stock Options [Member] | Stock Option and Incentive Plan 2012 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Exercise price as a percentage of fair market value on the date of grant | 100.00% |  |  |
Nonqualified Stock Options [Member] | Stock Option and Incentive Plan 2012 [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Exercise price as a percentage of fair market value on the date of grant | 85.00% |  |  |

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