Borrowed Funds (Components and Interest Expenses of Borrowed Funds) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total borrowed funds	$ 902,749	$ 920,542
Total interest expense on borrowed funds	24,711	24,216	$ 16,581
Advances from the FHLBB
Debt Instrument [Line Items]
Total borrowed funds	758,469	784,375
Total interest expense on borrowed funds	18,701	18,650	11,330
Subordinated debentures and notes
Debt Instrument [Line Items]
Total borrowed funds	83,591	83,433
Total interest expense on borrowed funds	5,206	5,181	5,081
Other borrowed funds
Debt Instrument [Line Items]
Total borrowed funds	60,689	52,734
Total interest expense on borrowed funds	$ 804	$ 385	$ 170