Shareholders' Equity - Minimum Capital Requirements were Considered Well Capitalized by FRB and FDIC (Details)	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total capital (to risk-weighted assets), Actual, Amount	$ 516,242,000	$ 506,239,000
Tier I capital (to risk-weighted assets), Actual, Amount	476,239,000	466,369,000
Common equity tier I capital (to risk-weighted assets), Actual, Amount	476,239,000	466,369,000
Tier I capital (to average assets), Actual, Amount	$ 476,239,000	$ 466,369,000
Total capital (to risk-weighted assets), Actual, Ratio	0.141	0.135
Tier I capital (to risk-weighted assets), Actual, Ratio	0.130	0.125
Common equity tier I capital (to risk-weighted assets), Actual, Ratio	0.130	0.125
Tier I capital (to average assets), Actual, Ratio	0.087	0.085
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Amount	$ 384,543,000	$ 393,285,000
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Amount	311,297,000	318,373,000
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Amount	256,362,000	262,190,000
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Amount	$ 218,011,000	$ 219,309,000
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Ratio	0.105	0.105
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Ratio	0.085	0.085
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Ratio	0.070	0.070
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Ratio	0.040	0.040
Cambridge Trust Company
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total capital (to risk-weighted assets), Actual, Amount	$ 494,631,000	$ 490,175,000
Tier I capital (to risk-weighted assets), Actual, Amount	454,627,000	450,305,000
Common equity tier I capital (to risk-weighted assets), Actual, Amount	454,627,000	450,305,000
Tier I capital (to average assets), Actual, Amount	$ 454,627,000	$ 450,305,000
Total capital (to risk-weighted assets), Actual, Ratio	0.135	0.131
Tier I capital (to risk-weighted assets), Actual, Ratio	0.124	0.120
Common equity tier I capital (to risk-weighted assets), Actual, Ratio	0.124	0.120
Tier I capital (to average assets), Actual, Ratio	0.083	0.082
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Amount	$ 384,507,000	$ 393,246,000
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Amount	311,268,000	318,342,000
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Amount	256,338,000	262,164,000
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Amount	$ 217,998,000	$ 219,296,000
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Ratio	0.105	0.105
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Ratio	0.085	0.085
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Ratio	0.070	0.070
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer, Ratio	0.040	0.040
Cambridge Trust Company | Minimum
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total capital (to risk-weighted assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Amount	$ 366,198,000	$ 374,520,000
Tier I capital (to risk-weighted assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Amount	292,958,000	299,616,000
Common equity tier I capital (to risk-weighted assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Amount	238,028,000	243,438,000
Tier I capital (to average assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Amount	$ 272,498,000	$ 274,120,000
Total capital (to risk-weighted assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	0.100	0.100
Tier I capital (to risk-weighted assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	0.080	0.080
Common equity tier I capital (to risk-weighted assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	0.065	0.065
Tier I capital (to average assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	0.050	0.050