Condensed Financial Statements of Parent Company - Condensed Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 61,335	$ 18,473
Other assets	42,291	27,629
Total assets	2,855,563	2,101,384
Shareholders’ Equity
Total shareholders' equity	286,561	167,026	$ 147,957	$ 134,671
Cambridge Bancorp [Member]
Assets
Cash and cash equivalents	1,680	4,412
Other assets	13
Investment in subsidiary	284,868	162,614
Total assets	286,561	167,026
Shareholders’ Equity
Total shareholders' equity	$ 286,561	$ 167,026