Commitments (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Unadvanced Commitment on Impaired Loan
Schedule of Commitments [Line Items]
Estimated losses attributable to unadvanced commitments on impaired loans	$ 430	$ 350
Commitments to extend credit
Schedule of Commitments [Line Items]
Off-balance sheet financial instruments, contractual amounts	1,393,782	1,344,687
Commitments to extend credit | Fixed Rate Loan Commitment
Schedule of Commitments [Line Items]
Off-balance sheet financial instruments, contractual amounts	134,300	68,500
Letters of credit
Schedule of Commitments [Line Items]
Off-balance sheet financial instruments, contractual amounts	$ 52,060	$ 44,665
Letters of credit | Maximum
Schedule of Commitments [Line Items]
Remaining term	5 years
Letters of credit | Minimum
Schedule of Commitments [Line Items]
Remaining term	1 month