Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets
Cash and due from banks	$ 64,544	$ 77,199
Federal funds sold and interest-bearing deposits in other banks	186,125	279,231
Total cash and cash equivalents	250,669	356,430
Securities available-for-sale, amortized cost $371,013 and $395,947, respectively	370,976	395,831
Securities held-to-maturity, fair value $1,760,498 and $1,668,827, respectively	1,817,633	1,701,233
Federal Home Loan Bank of Boston, stock at cost	20,050	21,779
Equity securities, amortized cost $ 1,635 and $1,635, respectively	1,654	1,663
Loans, net:
Construction and land development	17,583	18,931
Commercial and industrial	758,621	763,807
Municipal	104,044	106,599
Commercial real estate	726,440	732,491
Residential real estate	300,941	287,731
Consumer	18,635	18,458
Home equity	260,179	247,345
Overdrafts	704	582
Total loans, net	2,187,147	2,175,944
Less: allowance for loan losses	26,695	26,255
Net loans	2,160,452	2,149,689
Bank premises and equipment	23,220	23,527
Accrued interest receivable	10,844	11,179
Goodwill	2,714	2,714
Other assets	118,470	121,527
Total assets	4,776,682	4,785,572
Deposits:
Demand deposits	715,032	736,020
Savings and NOW deposits	1,409,157	1,367,358
Money market accounts	1,195,785	1,188,228
Time deposits	615,822	625,361
Total deposits	3,935,796	3,916,967
Securities sold under agreements to repurchase	141,560	158,990
Other borrowed funds	317,054	347,778
Subordinated debentures	36,083	36,083
Due to broker	10,011
Other liabilities	67,978	65,457
Total liabilities	4,508,482	4,525,275
Stockholders' Equity
Preferred Stock - $1.00 par value; 100,000 shares authorized; no shares issued and outstanding
Additional paid-in capital	12,292	12,292
Retained earnings	274,636	263,666
Stockholders' equity before adjustment of accumulated other comprehensive income (loss)	292,496	281,526
Unrealized losses on securities available-for-sale, net of taxes	(32)	(62)
Unrealized losses on securities transferred to held-to-maturity, net of taxes	(3,270)	(3,050)
Pension liability, net of taxes	(20,994)	(18,117)
Total accumulated other comprehensive loss, net of taxes	(24,296)	(21,229)
Total stockholders' equity	268,200	260,297
Total liabilities and stockholders' equity	4,776,682	4,785,572
Class A Common Stock [Member]
Stockholders' Equity
Common stock,Value	3,608	3,606
Total stockholders' equity	3,608	3,606
Class B Common Stock [Member]
Stockholders' Equity
Common stock,Value	1,960	1,962
Total stockholders' equity	$ 1,960	$ 1,962