Shareholders' Equity (Tables)

6 Months Ended

Jun. 30, 2019

Equity [Abstract]

Schedule of Minimum Capital Requirements Considered Well Capitalized by FRB and FDIC

As of June 30, 2019 and December 31, 2018, the Company and the Bank met all applicable minimum capital requirements and were considered “well-capitalized” by both the FRB and the FDIC.  

	Actual					Minimum Capital Required For Capital Adequacy					Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer (1)					Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions
	Amount		Ratio			Amount		Ratio			Amount		Ratio			Amount		Ratio
	(dollars in thousands)
At June 30, 2019
Cambridge Bancorp:
Total capital (to risk-weighted    assets)	$	222,152		11.8	%	$	150,732		8.0	%	$	197,836		10.5	%	N/A		N/A
Tier I capital (to risk-weighted   assets)		205,002		10.9	%		113,049		6.0	%		160,153		8.5	%	N/A		N/A
Common equity tier I capital    (to risk-weighted assets)		205,002		10.9	%		84,787		4.5	%		131,891		7.0	%	N/A		N/A
Tier I capital (to average    assets)		205,002		7.9	%		103,327		4.0	%		103,327		4.0	%	N/A		N/A
Cambridge Trust Company:
Total capital (to risk-weighted    assets)	$	218,012		11.6	%	$	150,732		8.0	%	$	197,836		10.5	%	$	188,415		10.0	%
Tier I capital (to risk-weighted    assets)		200,862		10.7	%		113,049		6.0	%		160,153		8.5	%		150,732		8.0	%
Common equity tier I capital    (to risk-weighted assets)		200,862		10.7	%		84,787		4.5	%		131,891		7.0	%		122,470		6.5	%
Tier I capital (to average    assets)		200,862		7.8	%		103,327		4.0	%		103,327		4.0	%		129,158		5.0	%

(1) The 2013 Capital Rules adopted by the Federal Reserve, Office of the Comptroller of the Currency, and the Federal Deposit Insurance Corporation implementing Basel III were fully phased-in effective January 1, 2019.

	Actual					Minimum Capital Required For Capital Adequacy					Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule					Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In					Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions
	Amount		Ratio			Amount		Ratio			Amount		Ratio			Amount		Ratio			Amount		Ratio
	(dollars in thousands)
At December 31, 2018
Cambridge Bancorp:
Total capital (to risk-weighted    assets)	$	189,888		13.2	%	$	114,666		8.0	%	$	141,541		9.875	%	$	150,500		10.5	%	N/A		N/A
Tier I capital (to risk-weighted    assets)		173,070		12.1	%		86,000		6.0	%		112,875		7.875	%		121,833		8.5	%	N/A		N/A
Common equity tier I capital    (to risk-weighted assets)		173,070		12.1	%		64,500		4.5	%		91,375		6.375	%		100,333		7.0	%	N/A		N/A
Tier I capital (to average    assets)		173,070		8.5	%		81,507		4.0	%		81,507		4.000	%		81,507		4.0	%	N/A		N/A
Cambridge Trust Company:
Total capital (to risk-weighted    assets)	$	185,507		12.9	%	$	114,666		8.0	%	$	141,541		9.875	%	$	150,500		10.5	%	$	143,333		10.0	%
Tier I capital (to risk-weighted    assets)		168,689		11.8	%		86,000		6.0	%		112,875		7.875	%		121,833		8.5	%		114,666		8.0	%
Common equity tier I capital    (to risk-weighted assets)		168,689		11.8	%		64,500		4.5	%		91,375		6.375	%		100,333		7.0	%		93,166		6.5	%
Tier I capital (to average    assets)		168,689		8.3	%		81,507		4.0	%		81,507		4.000	%		81,507		4.0	%		101,884		5.0	%