| Document and Entity Information | 12 Months Ended |
| Dec. 31, 2022 | |
| Cover [Abstract] | |
| Document Type | DEF 14A |
| Amendment Flag | false |
| Entity Registrant Name | CAMBRIDGE BANCORP |
| Entity Central Index Key | 0000711772 |
| Pay vs Performance Disclosure | 1 Months Ended | 12 Months Ended | ||||
| Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | |
| Pay vs Performance Disclosure [Table] | ||||||
| Pay vs Performance [Table Text Block] | Pay versus Performance The following is the Company’s pay versus performance disclosure, calculated in a manner consistent with Item 402(v) of Regulation S-K. Operating Return on Tangible Common Equity “ROTCE” was selected as the Company’s most important financial performance measure linking Compensation Actually Paid to our CEO and Other Named Executive Officers and Company performance. Value of initial fixed $100 investment Year Summary Compensation Table total for Chief Executive Officer Compensation actually paid to Chief Executive Officer (1,4) Average Summary Compensation Table total for NEOs other than CEO Average compensation actually paid to NEOs other than CEO (2,4) Cambridge Bancorp (3) ($) S&P U.S. Net Income (000) ($) Operating ROTCE 2022 $ 1,935,359 $ 1,628,278 $ 975,142 $ 629,527 $ 113.74 $ 95.12 $ 52,909 14.18 % 2021 $ 1,966,312 $ 2,475,604 $ 948,219 $ 1,040,614 $ 124.36 $ 118.43 $ 54,024 15.10 % 2020 $ 2,249,248 $ 2,517,537 $ 940,096 $ 975,893 $ 90.14 $ 86.69 $ 31,959 14.38 % (1) Denis Sheahan served as Chairman, President and Chief Executive Officer for each of the years presented in the table. (2) Messrs. Carotenuto, Fontaine and Millane and Ms. Pline served as NEOs for each of the years presented in the table. Mr. Mark Thompson, former President, also served as an NEO in 2020. (3) Cumulative total shareholder return (“TSR”) assumes an initial investment of $100 as of the market close on December 31, 2019. TSR for Cambridge Bancorp stock was ( 9.9 )% in 2020, 38.0 % in 2021 and ( 8.5 )% in 2022, for a cumulative three-year TSR of 13.7 %. A $100 investment in Cambridge Bancorp stock on December 31, 2019 would be valued at $ 113.74 as of December 31, 2022, which outperformed our peers as measured by the S&P U.S. BMI Banks Index. (4) Compensation actually paid to the CEO and NEOs for each of the years presented in the table are as follows: CEO Other NEO Average 2022 2021 2020 2022 2021 2020 Total Compensation as reported in the Summary Compensation Table ("SCT") $ 1,935,359 $ 1,966,312 $ 2,249,248 $ 975,142 $ 948,219 $ 940,096 Pension values as reported in SCT $ - $ ( 250,861 ) $ ( 424,782 ) $ - $ ( 3,244 ) $ ( 17,234 ) Fair value* of equity awards granted during fiscal year $ ( 800,000 ) $ ( 600,000 ) $ ( 800,000 ) $ ( 281,250 ) $ ( 210,938 ) $ ( 277,496 ) Pension value attributable to current year's service and any change in pension value attributable to plan amendments made in current year $ 404,445 $ 336,283 $ 237,850 $ - $ - $ - Fair value of equity compensation granted in current year - value at year-end $ 558,495 $ 573,707 $ 1,182,472 $ 124,216 $ 201,686 $ 365,239 Dividends paid on stock in the covered fiscal year prior to the vesting date that are not otherwise included in the total compensation for the covered fiscal year $ 45,973 $ 58,572 $ 99,973 $ 12,535 $ 16,997 $ 28,926 Change in fair value from end of prior fiscal year to end of current fiscal year for awards made in prior fiscal years that were unvested at end of current fiscal year $ ( 395,708 ) $ 200,697 $ 58,559 $ ( 137,198 ) $ 45,041 $ 11,893 Change in fair value from end of prior fiscal year to vesting date for awards made in prior fiscal years that vested during current fiscal year $ ( 120,286 ) $ 190,895 $ ( 85,783 ) $ ( 27,491 ) $ 42,852 $ ( 24,151 ) Fair value of awards forfeited in current fiscal year determined at the end of prior fiscal year $ - $ - $ - $ ( 36,427 ) $ - $ ( 51,381 ) Compensation Actually Paid $ 1,628,278 $ 2,475,604 $ 2,517,537 $ 629,527 $ 1,040,614 $ 975,893 *Note: Fair value was computed in accordance with the Company’s methodology used for financial reporting purposes. | |||||
| Company Selected Measure Name | Operating ROTCE | |||||
| Named Executive Officers, Footnote [Text Block] | Denis Sheahan served as Chairman, President and Chief Executive Officer for each of the years presented in the table. (2) Messrs. Carotenuto, Fontaine and Millane and Ms. Pline served as NEOs for each of the years presented in the table. Mr. Mark Thompson, former President, also served as an NEO in 2020. | |||||
| PEO Total Compensation Amount | $ 1,935,359 | $ 1,966,312 | $ 2,249,248 | |||
| PEO Actually Paid Compensation Amount | 1,628,278 | 2,475,604 | 2,517,537 | |||
| Non-PEO NEO Average Total Compensation Amount | 975,142 | 948,219 | 940,096 | |||
| Non-PEO NEO Average Compensation Actually Paid Amount | $ 629,527 | 1,040,614 | 975,893 | |||
| Compensation Actually Paid vs. Total Shareholder Return [Text Block] | ompensation Actually Paid (CAP) and TSR | |||||
| Compensation Actually Paid vs. Net Income [Text Block] | tually Paid (CAP) and Net Income | |||||
| Compensation Actually Paid vs. Company Selected Measure [Text Block] | Compensation Actually Paid (CAP) and Operating ROTCE | |||||
| Tabular List [Table Text Block] | The following table lists either the required disclosure metrics, or the most important financial performance measures used by the Company to link compensation actually paid to our named executive officers to company performance. • Total Shareholder Return (TSR) • Operating Return on Tangible Common Equity (ROTCE) • Operating Income • Relative Return on Assets • Operating Diluted Earnings per Share (EPS) growth | |||||
| Total Shareholder Return Amount | $ 113.74 | 124.36 | 90.14 | |||
| Peer Group Total Shareholder Return Amount | 95.12 | 118.43 | 86.69 | |||
| Net Income (Loss) | $ 52,909,000 | $ 54,024,000 | $ 31,959,000 | |||
| Company Selected Measure Amount | 0.1418 | 0.1510 | 0.1438 | |||
| PEO Name | Denis Sheahan | Denis Sheahan | Denis Sheahan | |||
| Total Shareholder Rtn Percentage | (8.50%) | 38% | (9.90%) | |||
| Cumulative Total Shareholder Return Percentage | 13.70% | |||||
| Adj To Comp Fn [TextBlock] | (4) Compensation actually paid to the CEO and NEOs for each of the years presented in the table are as follows: CEO Other NEO Average 2022 2021 2020 2022 2021 2020 Total Compensation as reported in the Summary Compensation Table ("SCT") $ 1,935,359 $ 1,966,312 $ 2,249,248 $ 975,142 $ 948,219 $ 940,096 Pension values as reported in SCT $ - $ ( 250,861 ) $ ( 424,782 ) $ - $ ( 3,244 ) $ ( 17,234 ) Fair value* of equity awards granted during fiscal year $ ( 800,000 ) $ ( 600,000 ) $ ( 800,000 ) $ ( 281,250 ) $ ( 210,938 ) $ ( 277,496 ) Pension value attributable to current year's service and any change in pension value attributable to plan amendments made in current year $ 404,445 $ 336,283 $ 237,850 $ - $ - $ - Fair value of equity compensation granted in current year - value at year-end $ 558,495 $ 573,707 $ 1,182,472 $ 124,216 $ 201,686 $ 365,239 Dividends paid on stock in the covered fiscal year prior to the vesting date that are not otherwise included in the total compensation for the covered fiscal year $ 45,973 $ 58,572 $ 99,973 $ 12,535 $ 16,997 $ 28,926 Change in fair value from end of prior fiscal year to end of current fiscal year for awards made in prior fiscal years that were unvested at end of current fiscal year $ ( 395,708 ) $ 200,697 $ 58,559 $ ( 137,198 ) $ 45,041 $ 11,893 Change in fair value from end of prior fiscal year to vesting date for awards made in prior fiscal years that vested during current fiscal year $ ( 120,286 ) $ 190,895 $ ( 85,783 ) $ ( 27,491 ) $ 42,852 $ ( 24,151 ) Fair value of awards forfeited in current fiscal year determined at the end of prior fiscal year $ - $ - $ - $ ( 36,427 ) $ - $ ( 51,381 ) Compensation Actually Paid $ 1,628,278 $ 2,475,604 $ 2,517,537 $ 629,527 $ 1,040,614 $ 975,893 *Note: Fair value was computed in accordance with the Company’s methodology used for financial reporting purposes. | |||||
| Measure [Axis]: 1 | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Non-GAAP Measure Description [Text Block] | Cumulative total shareholder return (“TSR”) assumes an initial investment of $100 as of the market close on December 31, 2019. TSR for Cambridge Bancorp stock was ( 9.9 )% in 2020, 38.0 % in 2021 and ( 8.5 )% in 2022, for a cumulative three-year TSR of 13.7 %. A $100 investment in Cambridge Bancorp stock on December 31, 2019 would be valued at $ 113.74 as of December 31, 2022, which outperformed our peers as measured by the S&P U.S. BMI Banks Index. | |||||
| PEO [Member] | Measure [Axis]: 1 | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Measure Name | Total Shareholder Return (TSR) | |||||
| PEO [Member] | Measure [Axis]: 2 | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Measure Name | Operating Return on Tangible Common Equity (ROTCE) | |||||
| PEO [Member] | Measure [Axis]: 3 | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Measure Name | Operating Income | |||||
| PEO [Member] | Measure [Axis]: 4 | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Measure Name | Relative Return on Assets | |||||
| PEO [Member] | Measure [Axis]: 5 | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Measure Name | Operating Diluted Earnings per Share (EPS) growth | |||||
| PEO [Member] | Pension Values as Reported in SCT [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | $ (250,861) | $ (424,782) | ||||
| PEO [Member] | Fair Value of Equity Awards Granted During Fiscal Year [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | $ (800,000) | (600,000) | (800,000) | |||
| PEO [Member] | Pension Value Attributable to Current Year's Service and Any Change in Pension Value Attributable to Plan Amendments Made in Current Year [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | 404,445 | 336,283 | 237,850 | |||
| PEO [Member] | Fair Value of Equity Compensation Granted in Current Year - Value at Year-end [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | 558,495 | 573,707 | 1,182,472 | |||
| PEO [Member] | Dividends Paid on Stock in the Covered Fiscal Year Prior to the Vesting Date That Are Not Otherwise Included in the Total Compensation for the Covered Fiscal Year [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | 45,973 | 58,572 | 99,973 | |||
| PEO [Member] | Change in Fair Value From End of Prior Fiscal Year to End of Current Fiscal Year for Awards Made in Prior Fiscal Years That Were Unvested at End of Current Fiscal Year [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | (395,708) | 200,697 | 58,559 | |||
| PEO [Member] | Change in Fair Value From End of Prior Fiscal Year to Vesting Date for Awards Made in Prior Fiscal Years That Vested During Current Fiscal Year [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | (120,286) | 190,895 | (85,783) | |||
| Non-PEO NEO [Member] | Pension Values as Reported in SCT [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | (3,244) | (17,234) | ||||
| Non-PEO NEO [Member] | Fair Value of Equity Awards Granted During Fiscal Year [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | (281,250) | (210,938) | (277,496) | |||
| Non-PEO NEO [Member] | Fair Value of Equity Compensation Granted in Current Year - Value at Year-end [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | 124,216 | 201,686 | 365,239 | |||
| Non-PEO NEO [Member] | Dividends Paid on Stock in the Covered Fiscal Year Prior to the Vesting Date That Are Not Otherwise Included in the Total Compensation for the Covered Fiscal Year [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | 12,535 | 16,997 | 28,926 | |||
| Non-PEO NEO [Member] | Change in Fair Value From End of Prior Fiscal Year to End of Current Fiscal Year for Awards Made in Prior Fiscal Years That Were Unvested at End of Current Fiscal Year [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | (137,198) | 45,041 | 11,893 | |||
| Non-PEO NEO [Member] | Change in Fair Value From End of Prior Fiscal Year to Vesting Date for Awards Made in Prior Fiscal Years That Vested During Current Fiscal Year [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | (27,491) | $ 42,852 | (24,151) | |||
| Non-PEO NEO [Member] | Fair value of awards forfeited in current fiscal year determined at the end of prior fiscal year [Member] | ||||||
| Pay vs Performance Disclosure [Table] | ||||||
| Adjustment to Compensation Amount | $ (36,427) | $ (51,381) | ||||
