Commitments (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Unadvanced Commitment on Impaired Loan
Schedule of Commitments [Line Items]
Estimated losses attributable to unadvanced commitments on impaired loans	$ 4,900	$ 400
Commitments to extend credit
Schedule of Commitments [Line Items]
Off-balance sheet financial instruments, contractual amounts	1,659,225	1,469,413
Commitments to extend credit | Fixed Rate Loan Commitment
Schedule of Commitments [Line Items]
Off-balance sheet financial instruments, contractual amounts	161,300	144,800
Letters of credit
Schedule of Commitments [Line Items]
Off-balance sheet financial instruments, contractual amounts	$ 51,798	$ 47,969
Letters of credit | Maximum
Schedule of Commitments [Line Items]
Remaining term	4 years
Letters of credit | Minimum
Schedule of Commitments [Line Items]
Remaining term	1 month