Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities
Net income	$ 34,666	$ 32,825
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation of property, plant and equipment	50,051	48,594
Other amortization	2,372	1,928
Provision for loan losses	3,907	4,766
Loans receivable originated and purchased, held for sale	(35,725)	(42,719)
Proceeds from sale of loans receivable, held for sale	40,588	40,363
Deferred income taxes	10,096	13,008
Share-based compensation expense	1,056	1,013
Allowance for equity funds used during construction	(2,399)	(1,739)
Other	(347)	1,702
Changes in assets and liabilities
Decrease (increase) in accounts receivable and unbilled revenues, net	(12,337)	28,108
Decrease (increase) in fuel oil stock	(7,444)	22,812
Decrease in regulatory assets	5,909	1,585
Increase in accounts, interest and dividends payable	71,846	30,135
Change in prepaid and accrued income taxes, tax credits and utility revenue taxes	(42,175)	(14,343)
Increase in defined benefit pension and other postretirement benefit plans liability	1,012	137
Change in other assets and liabilities	(27,142)	2,797
Net cash provided by operating activities	93,934	170,972
Cash flows from investing activities
Available-for-sale investment securities purchased	(171,878)	(122,387)
Principal repayments on available-for-sale investment securities	48,200	48,819
Purchase of stock from Federal Home Loan Bank	(488)	(1,373)
Redemption of stock from Federal Home Loan Bank	0	833
Net decrease (increase) in loans held for investment	890	(28,137)
Proceeds from sale of commercial loans	13,493	0
Proceeds from sale of real estate acquired in settlement of loans	185	232
Capital expenditures	(138,185)	(127,818)
Contributions in aid of construction	10,650	13,761
Other	5,709	819
Net cash used in investing activities	(231,424)	(215,251)
Cash flows from financing activities
Net increase in deposit liabilities	126,161	114,678
Net increase (decrease) in short-term borrowings with original maturities of three months or less	2,300	(7,578)
Net increase in retail repurchase agreements	21,071	19,041
Proceeds from other bank borrowings	0	20,835
Repayments of other bank borrowings	(13,534)	(39,369)
Proceeds from issuance of long-term debt	0	75,000
Repayment of long-term debt	0	(75,000)
Withheld shares for employee taxes on vested share-based compensation	(3,687)	(2,335)
Net proceeds from issuance of common stock	0	3,022
Common stock dividends	(33,713)	(27,716)
Preferred stock dividends of subsidiaries	(473)	(473)
Other	(4,857)	(1,561)
Net cash provided by financing activities	93,268	78,544
Net increase (decrease) in cash and cash equivalents	(44,222)	34,265
Cash and cash equivalents, beginning of period	278,452	300,478
Cash and cash equivalents, end of period	$ 234,230	$ 334,743