Consolidated Statements Of Cash Flow - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net income	$ 49,072	$ 51,737
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	34,026	32,595
Deferred income taxes	2,681	1,436
Provision for doubtful accounts	1,111	817
Stock-based compensation	1,312	806
Loss (gain) on sale of utility system and market-based business unit	278	(1,215)
Gain on sale of other assets	(269)	(207)
Net change in receivables, inventory and prepayments	5,729	5,680
Net change in payables, accrued interest, accrued taxes and other accrued liabilities	(4,519)	4,880
Pension and other postretirement benefits contributions	(7,711)	(2,714)
Other	(507)	1,023
Net cash flows from operating activities	81,203	94,838
Cash flows from investing activities:
Property, plant and equipment additions, including the debt component of allowance for funds used during construction of $721 and $580	(94,562)	(72,984)
Acquisitions of utility systems and other, net	(220)	(4,461)
Net proceeds from the sale of utility system and other assets	639	2,853
Other	(171)	(40)
Net cash flows used in investing activities	(94,314)	(74,632)
Cash flows from financing activities:
Customers' advances and contributions in aid of construction	1,585	1,273
Repayments of customers' advances	(511)	(349)
Net proceeds of short-term debt	21,197	11,320
Proceeds from long-term debt	117,879	96,314
Repayments of long-term debt	(89,666)	(80,341)
Change in cash overdraft position	(2,403)	(17,250)
Proceeds from issuing common stock	360	332
Proceeds from exercised stock options	1,536	2,816
Stock-based compensation windfall tax benefits		979
Repurchase of common stock	(2,053)	(2,827)
Dividends paid on common stock	(33,945)	(31,513)
Other	(206)	(208)
Net cash flows from (used in) financing activities	13,773	(19,454)
Net change in cash and cash equivalents	662	752
Cash and cash equivalents at beginning of period	3,763	3,229
Cash and cash equivalents at end of period	4,425	3,981
Non-cash investing activities:
Property, plant and equipment additions purchased at the period end, but not yet paid for	27,084	19,052
Non-cash customer advances and contributions in aid of construction	$ 4,282	$ 5,425