Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities
Net income	$ 69,640	$ 64,831
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation of property, plant and equipment	62,990	61,427
Other amortization	9,425	10,951
Provision for credit losses	(3,263)	(8,435)
Loans originated, held for sale	(73,931)	(162,901)
Proceeds from sale of loans, held for sale	75,629	170,862
Gain on sales of investment securities, net and equity-method investment	(8,123)	(528)
Gain on sale of loans, net	(1,077)	(4,300)
Deferred income taxes	(5,255)	(2,196)
Share-based compensation expense	2,117	2,602
Allowance for equity funds used during construction	(2,409)	(2,191)
Other	(2,552)	(3,519)
Changes in assets and liabilities
Decrease in accounts receivable and unbilled revenues, net	4,454	5,664
Increase in fuel oil stock	(35,333)	(16,400)
Increase in regulatory assets	(5,089)	(14,869)
Increase (decrease) in regulatory liabilities	5,520	(4,716)
Increase in accounts, interest and dividends payable	71,490	7,677
Change in prepaid and accrued income taxes, tax credits and utility revenue taxes	(14,928)	(25,513)
Decrease in defined benefit pension and other postretirement benefit plans liability	(1,309)	(2,621)
Change in other assets and liabilities	(55,411)	(34,095)
Net cash provided by operating activities	92,585	41,730
Cash flows from investing activities
Available-for-sale investment securities purchased	(291,168)	(781,992)
Principal repayments on available-for-sale investment securities	104,654	184,755
Proceeds from sale of available-for-sale investment securities	0	197,354
Purchases of held-to-maturity investment securities	0	(88,262)
Proceeds from repayments or maturities of held-to-maturity investment securities	4,547	20,185
Purchase of stock from Federal Home Loan Bank	0	(22,296)
Redemption of stock from Federal Home Loan Bank	0	20,976
Net decrease in loans held for investment	28,076	23,922
Capital expenditures	(79,163)	(74,079)
Contributions to low income housing investments	0	(3,205)
Other	5,340	4,622
Net cash used in investing activities	(227,714)	(518,020)
Cash flows from financing activities
Net increase in deposit liabilities	117,060	358,337
Net increase in short-term borrowings with original maturities of three months or less	17,493	35,751
Net increase in other bank borrowings with original maturities of three months or less	49,080	13,015
Repayment of short-term debt	0	(65,000)
Proceeds from issuance of long-term debt	7,312	161,800
Repayment of long-term debt	(13,446)	(50,699)
Withheld shares for employee taxes on vested share-based compensation	(3,065)	(1,997)
Common stock dividends	(38,301)	(37,156)
Preferred stock dividends of subsidiaries	(473)	(473)
Other	(4,377)	(4,621)
Net cash provided by financing activities	131,283	408,957
Net decrease in cash, cash equivalents and restricted cash	(3,846)	(67,333)
Cash, cash equivalents and restricted cash, beginning of period	311,462	358,979
Cash, cash equivalents and restricted cash, end of period	307,616	291,646
Less: Restricted cash	(5,912)	(14,067)
Cash and cash equivalents, end of period	$ 301,704	$ 277,579