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Pay vs Performance Disclosure - USD ($) | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Pay vs Performance Disclosure [Table] |  |  |  |
Pay vs Performance [Table Text Block] |  |
|  |  |  |  |  | Average Summary |  | Average |  | Value of Initial Fixed $100 Investment Based On: |  |  |  |
Year (a) |  | Summary Compensation Table Total for CEO (b) |  | Compensation Actually Paid to CEO (c) |  | Compensation Table Total for non-CEO NEOs (d) |  | Compensation Actually Paid to non-CEO NEOs (e) |  | Total Shareholder Return (f) |  | Peer Group Total Shareholder Return (g) |  | Net Income (In Millions) (h) |  | Income Before Income Taxes (In Millions) (i)
2022 |  | $ | 1,154,726 |  |  | $ | 38,867 |  |  | $ | 452,477 |  |  | $ | 284,597 |  |  | $ | 128.86 |  |  | $ | 120.09 |  |  | $ | 42.429 |  |  | $ | 44.400 |
2021 |  | $ | 1,290,444 |  |  | $ | 3,173,051 |  |  | $ | 490,567 |  |  | $ | 782,328 |  |  | $ | 194.55 |  |  | $ | 132.92 |  |  | $ | 36.423 |  |  | $ | 31.685 |
2020 |  | $ | 1,781,494 |  |  | $ | 1,714,156 |  |  | $ | 677,013 |  |  | $ | 526,936 |  |  | $ | 115.79 |  |  | $ | 101.42 |  |  | $ | 38.305 |  |  | $ | 28.118 |
Column (b) Reflects compensation amounts reported in the “Summary Compensation Table” for our CEO, Dennis Doll, for the respective years shown. Column (c) “Compensation actually paid” to our CEO in each of 2022, 2021 and 2020 reflects the respective amounts set forth in column (b) of the compensation table above, adjusted as set forth in the compensation calculation table below, as determined in accordance with SEC rules. The dollar amounts reflected in column (b) of the table above do not reflect the actual amount of compensation earned by or paid to our CEO during the applicable year. For information regarding the decisions made by our Compensation Committee in regards to the CEO’s compensation for each fiscal year, please see the CD&A sections of the proxy statements reporting pay for the fiscal years covered in the table above. The aggregate change in actuarial present value of accumulated benefit under pension plans reflects the amount reported for the applicable year in the Summary Compensation Table. Column (d) Reflects compensation information for our NEOs other than the CEO as described in the CD&A of this proxy statement. 2022: A. Bruce O’Connor, Jay L. Kooper, Robert K. Fullagar, Georgia M. Simpson 2021: A. Bruce O’Connor, Bernadette M. Sohler, Jay L. Kooper, Lorrie B. Ginegaw 2020: A. Bruce O’Connor, Bernadette M. Sohler, Lorrie B. Ginegaw, Jay L. Kooper Column (e) Average “compensation actually paid” for our non-CEO NEOs in each of 2022, 2021 and 2020 reflects the respective amounts set forth in column (d) of the table above, adjusted as set forth in the compensation calculation table below, as determined in accordance with SEC rules. The dollar amounts reflected in column (d) of the table above do not reflect the actual amount of compensation earned by or paid to our non-CEO NEOs during the applicable year. For information regarding the decisions made by our Compensation Committee in regards to the non-CEO NEOs compensation for each fiscal year, please see the CD&A sections of the proxy statements reporting pay for the fiscal years covered in the table above. Column (f) For the relevant fiscal year, represents the cumulative total shareholder return (TSR) of Middlesex for the measurement periods ending on December 31 of each of 2022, 2021 and 2020, respectively. Column (g) For the relevant fiscal year, represents the cumulative TSR of the Peer Group for the measurement periods ending on December 31 of each of 2022, 2021 and 2020, respectively. Peer Group companies currently include American States Water Company, Artesian Resources Corp., California Water Service Group, Global Water Resources Inc., SJW Corp., and York Water Company. Column (h) Reflects Net Income in the Company’s Consolidated Income Statements included in the Company’s Annual Reports on Form 10-K for each of the years ended December 31, 2022, 2021 and 2020. Column (i) Reflects Income Before Income Taxes in the Company’s Consolidated Income Statements included in the Company’s Annual Report on Form 10-K for each of the years ended December 31, 2022, 2021 and 2020. |  |
Named Executive Officers, Footnote [Text Block] |  | Reflects compensation amounts reported in the “Summary Compensation Table” for our CEO, Dennis Doll, for the respective years shown. |  |
Peer Group Issuers, Footnote [Text Block] |  | For the relevant fiscal year, represents the cumulative total shareholder return (TSR) of Middlesex for the measurement periods ending on December 31 of each of 2022, 2021 and 2020, respectively. |  |
PEO Total Compensation Amount | [1] | $ 1,154,726 | $ 1,290,444 | $ 1,781,494
PEO Actually Paid Compensation Amount | [2] | $ 38,867 | 3,173,051 | 1,714,156
Adjustment To PEO Compensation, Footnote [Text Block] |  |
Year |  | Summary Compensation Table Total for CEO |  | Summary Compensation Table Equity Awards for CEO |  | Equity Awards Adjustment for CEO |  | Summary Compensation Table Change in Pension Value for CEO |  | Pension Service Cost Adjustment for CEO |  | Total Compensation Actually Paid to CEO
2022 |  | $ | 1,154,726 |  |  | $ | (400,000 | ) |  | $ | (1,008,164 | ) |  | $ | — |  |  | $ | 292,314 |  |  | $ | 38,876 |
2021 |  | $ | 1,290,444 |  |  | $ | (400,000 | ) |  | $ | 2,176,122 |  |  | $ | (174,119 | ) |  | $ | 280,604 |  |  | $ | 3,173,051 |
2020 |  | $ | 1,781,494 |  |  | $ | (400,000 | ) |  | $ | 758,543 |  |  | $ | (679,154 | ) |  | $ | 253,273 |  |  | $ | 1,714,156 |
Fair Value of Equity Awards for CEO |  | 2022 |  | 2021 |  | 2020
Year End Fair Value of Current Year Equity Award |  | $ | 299,182 |  |  | $ | 608,959 |  |  | $ | 403,368 |
Year End Change in Fair Value of Prior Year Equity Awards |  | $ | (1,184,082 | ) |  | $ | 1,507,984 |  |  | $ | 311,473 |
Change in Fair Value of Prior Year Equity Awards Vesting in Current Year |  | $ | (123,264 | ) |  | $ | 59,179 |  |  | $ | 43,702 |
Total Equity Awards Adjustments for CEO |  | $ | (1,008,164 | ) |  | $ | 2,176,122 |  |  | $ | 758,543 |
Non-PEO NEO Average Total Compensation Amount | [3] | $ 452,477 | 490,567 | 677,013
Non-PEO NEO Average Compensation Actually Paid Amount | [4] | $ 284,597 | 782,328 | 526,936
Adjustment to Non-PEO NEO Compensation Footnote [Text Block] |  |
Year |  | Average Summary Compensation Table Total for non-CEO NEOs |  | Average Summary Compensation Table Equity Awards for non-CEO NEOs |  | Average Equity Awards Adjustment for non-CEO NEOs |  | Average Summary Compensation Table Change in Pension Value for non-CEO NEOs |  | Average Pension Service Cost Adjustment for non-CEO NEOs |  | Average Total Compensation Actually Paid to non-CEO NEOs
2022 |  | $ | 452,477 |  |  | $ | (92,500 | ) |  | $ | (120,479 | ) |  | $ | — |  |  | $ | 45,098 |  |  | $ | 284,597 |
2021 |  | $ | 490,567 |  |  | $ | (88,750 | ) |  | $ | 390,457 |  |  | $ | (78,407 | ) |  | $ | 68,461 |  |  | $ | 782,328 |
2020 |  | $ | 677,013 |  |  | $ | (88,750 | ) |  | $ | 153,174 |  |  | $ | (273,752 | ) |  | $ | 59,252 |  |  | $ | 526,936 |
Fair Value of Average Equity Awards for non-CEO NEOs |  | 2022 |  | 2021 |  | 2020
Year End Fair Value of Current Year Equity Award |  | $ | 67,342 |  |  | $ | 135,097 |  |  | $ | 100,462 |
Year End Change in Fair Value of Prior Year Equity Awards |  | $ | (175,221 | ) |  | $ | 246,026 |  |  | $ | 46,124 |
Change in Fair Value of Prior Year Equity Awards Vesting in Current Year |  | $ | (12,600 | ) |  | $ | 9,334 |  |  | $ | 6,588 |
Total Equity Awards Adjustments non-CEO NEOs |  | $ | (120,479 | ) |  | $ | 390,457 |  |  | $ | 153,174 |
Compensation Actually Paid vs. Total Shareholder Return [Text Block] |  |  |  |
Compensation Actually Paid vs. Net Income [Text Block] |  |  |  |
Tabular List [Table Text Block] |  | Pay for Performance Alignment The Company has identified Income Before Taxes, as referenced in the table at the top of page 32, as the most important financial performance measure. As income taxes are largely a function of taxable income, management has a greater ability to drive financial performance affecting those income statement line items, which are separate and apart from income taxes, than income taxes themselves. Listed below are the financial performance measures, which in our assessment, represent additional important financial performance measures we use to link compensation actually paid to our NEOs, for 2022, to company performance.
| • | Return on Average Common Equity
| • | Net Income
| • | Total Shareholder Return
Total Shareholder Return Amount | [5] | $ 128.86 | 194.55 | 115.79
Peer Group Total Shareholder Return Amount | [6] | 120.09 | 132.92 | 101.42
Net Income (Loss) | [7] | $ 42,429,000 | 36,423,000 | 38,305,000
PEO Name |  | Dennis Doll |  |
Results of Operations, Income before Income Taxes | [8] | $ 44,400,000 | 31,685,000 | 28,118,000
Measure [Axis]: 1 |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Measure Name |  | Return on Average Common Equity |  |
Measure [Axis]: 2 |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Measure Name |  | Net Income |  |
Measure [Axis]: 3 |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Measure Name |  | Total Shareholder Return |  |
CEO [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | $ (1,008,164) | 2,176,122 | 758,543
CEO [Member] | Summary Compensation Table Total for CEO [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | 1,154,726 | 1,290,444 | 1,781,494
CEO [Member] | Summary Compensation Table Equity Awards for CEO [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | (400,000) | (400,000) | (400,000)
CEO [Member] | Equity Awards Adjustment for CEO [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | (1,008,164) | 2,176,122 | 758,543
CEO [Member] | Summary Compensation Table Change in Pension Value for CEO [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  |  | (174,119) | (679,154)
CEO [Member] | Pension Service Cost Adjustment for CEO [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | 292,314 | 280,604 | 253,273
CEO [Member] | Total Compensation Actually Paid to CEO [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | 38,876 | 3,173,051 | 1,714,156
CEO [Member] | Year End Fair Value of Current Year Equity Award [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | 299,182 | 608,959 | 403,368
CEO [Member] | Year End Change in Fair Value of Prior Year Equity Awards [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | (1,184,082) | 1,507,984 | 311,473
CEO [Member] | Change in Fair Value of Prior Year Equity Awards Vesting in Current Year [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | (123,264) | 59,179 | 43,702
Non-CEO [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | (120,479) | 390,457 | 153,174
Non-CEO [Member] | Year End Fair Value of Current Year Equity Award [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | 67,342 | 135,097 | 100,462
Non-CEO [Member] | Year End Change in Fair Value of Prior Year Equity Awards [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | (175,221) | 246,026 | 46,124
Non-CEO [Member] | Change in Fair Value of Prior Year Equity Awards Vesting in Current Year [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | (12,600) | 9,334 | 6,588
Non-CEO [Member] | Average Summary Compensation Table Total for non-CEO NEOs [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | 452,477 | 490,567 | 677,013
Non-CEO [Member] | Average Summary Compensation Table Equity Awards for non-CEO NEOs [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | (92,500) | (88,750) | (88,750)
Non-CEO [Member] | Average Equity Awards Adjustment for non-CEO NEOs [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | (120,479) | 390,457 | 153,174
Non-CEO [Member] | Average Summary Compensation Table Change in Pension Value for non-CEO NEOs [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  |  | (78,407) | (273,752)
Non-CEO [Member] | Average Pension Service Cost Adjustment for non-CEO NEOs [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | 45,098 | 68,461 | 59,252
Non-CEO [Member] | Average Total Compensation Actually Paid to non-CEO NEOs [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Adjustment to Compensation Amount |  | $ 284,597 | $ 782,328 | $ 526,936
[1] | Reflects compensation amounts reported in the “Summary Compensation Table” for our CEO, Dennis Doll, for the respective years shown.
[2] | “Compensation actually paid” to our CEO in each of 2022, 2021 and 2020 reflects the respective amounts set forth in column (b) of the compensation table above, adjusted as set forth in the compensation calculation table below, as determined in accordance with SEC rules. The dollar amounts reflected in column (b) of the table above do not reflect the actual amount of compensation earned by or paid to our CEO during the applicable year. For information regarding the decisions made by our Compensation Committee in regards to the CEO’s compensation for each fiscal year, please see the CD&A sections of the proxy statements reporting pay for the fiscal years covered in the table above. The aggregate change in actuarial present value of accumulated benefit under pension plans reflects the amount reported for the applicable year in the Summary Compensation Table.
[3] | Reflects compensation information for our NEOs other than the CEO as described in the CD&A of this proxy statement. 2022: A. Bruce O’Connor, Jay L. Kooper, Robert K. Fullagar, Georgia M. Simpson 2021: A. Bruce O’Connor, Bernadette M. Sohler, Jay L. Kooper, Lorrie B. Ginegaw 2020: A. Bruce O’Connor, Bernadette M. Sohler, Lorrie B. Ginegaw, Jay L. Kooper
[4] | Average “compensation actually paid” for our non-CEO NEOs in each of 2022, 2021 and 2020 reflects the respective amounts set forth in column (d) of the table above, adjusted as set forth in the compensation calculation table below, as determined in accordance with SEC rules. The dollar amounts reflected in column (d) of the table above do not reflect the actual amount of compensation earned by or paid to our non-CEO NEOs during the applicable year. For information regarding the decisions made by our Compensation Committee in regards to the non-CEO NEOs compensation for each fiscal year, please see the CD&A sections of the proxy statements reporting pay for the fiscal years covered in the table above.
[5] | For the relevant fiscal year, represents the cumulative total shareholder return (TSR) of Middlesex for the measurement periods ending on December 31 of each of 2022, 2021 and 2020, respectively.
[6] | For the relevant fiscal year, represents the cumulative TSR of the Peer Group for the measurement periods ending on December 31 of each of 2022, 2021 and 2020, respectively. Peer Group companies currently include American States Water Company, Artesian Resources Corp., California Water Service Group, Global Water Resources Inc., SJW Corp., and York Water Company.
[7] | Reflects Net Income in the Company’s Consolidated Income Statements included in the Company’s Annual Reports on Form 10-K for each of the years ended December 31, 2022, 2021 and 2020.
[8] | Reflects Income Before Income Taxes in the Company’s Consolidated Income Statements included in the Company’s Annual Report on Form 10-K for each of the years ended December 31, 2022, 2021 and 2020.

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