Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 39,699	$ 36,213	$ 22,301
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Gain on sales of mortgage loans	(412)		(370)
Gain on sale of fixed assets			(11)
Net loss on other real estate owned	79
Net gains on sales of securities	(61)	(302)	(47)
Net (gain) loss on equity securities	(92)	67
Provision for loan losses	1,250	1,350	1,790
Deferred tax (expense) benefit	(2,135)	(1,766)	6,918
Net depreciation and amortization	(2,382)	885	3,047
Decrease (increase) in accrued interest receivable	1,296	(3,227)	(1,534)
(Increase) decrease in other assets	8,532	2,326	(16,310)
Increase in other liabilities	2,075	5,242	5,802
Net cash provided by operating activities	47,849	40,788	21,586
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from maturities of short-term investments			5,284
Purchase of short-term investments			(2,101)
Proceeds from redemptions of Federal Home Loan Bank of Boston stock	14,380	18,388	10,127
Purchase of Federal Home Loan Bank of Boston stock	(15,877)	(14,583)	(10,864)
Proceeds from calls/maturities of securities available-for-sale	144,739	215,406	259,388
Proceeds from sales of securities available-for-sale	16,285	27,517	18,180
Purchase of securities available-for-sale	(85,123)	(183,588)	(175,147)
Proceeds from calls/maturities of securities held-to-maturity	458,915	234,741	293,221
Purchase of securities held-to-maturity	(757,997)	(576,140)	(337,773)
Proceeds from sales of securities held-to-maturity	1,193
Proceeds from life insurance policies	5,461	375	115
Proceeds from sales of portfolio loans	22,120		26,701
Net increase in loans	(162,415)	(110,874)	(278,242)
Bank owned life insurance purchases	(33,664)
Proceeds from sales of other real estate owned	2,146
Proceeds from sales of fixed assets			11
Capital expenditures	(13,144)	(3,601)	(3,244)
Net cash used in investing activities	(402,981)	(392,359)	(194,344)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net (decrease) increase in time deposit accounts	(5,132)	(64,782)	147,002
Net decrease (increase) in demand, savings, money market and NOW deposits	(1,721)	554,779	116,747
Cash dividends	(2,207)	(2,203)	(2,200)
Net increase (decrease) in securities sold under agreements to repurchase	111,805	(4,750)	(23,290)
Net increase (decrease) in other borrowed funds	168,577	(145,400)	54,778
Net cash provided by financing activities	271,322	337,644	293,037
Net (decrease) increase in cash and cash equivalents	(83,810)	(13,927)	120,279
Cash and cash equivalents at beginning of period	342,503	356,430	236,151
Cash and cash equivalents at end of period	258,693	342,503	356,430
Cash paid (received) during the period for:
Interest	63,345	44,289	27,731
Income tax refunds	(6,504)
Income taxes		590	5,330
Change in unrealized losses on securities available-for-sale, net of taxes	(314)	109	505
Change in unrealized losses on securities transferred to held-to-maturity, net of taxes	753	1,086	1,034
Pension liability adjustment, net of taxes	$ (5,789)	4,937	$ (1,384)
Transfer of loans to other real estate owned		$ 2,225