CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
OPERATING ACTIVITIES:
Net Income	$ 202,120	$ 196,960	$ 162,703
Items not affecting cash:
Depreciation and depletion	172,923	174,476	166,137
Amortization of debt issuance costs, discount and deferred hedge gain	4,648	4,645	4,794
Stock-based compensation costs	8,007	7,683	5,563
Equity portion of allowance for funds used during construction	(5,768)	(4,165)	(5,701)
(Gain) loss on disposition of assets	(188)	87	(415)
Deferred income taxes	(13,864)	(13,189)	12,363
Changes in current assets and liabilities:
Accounts receivable	(5,032)	19,909	(22,726)
Inventories	(3,110)	1,617	(3,226)
Other current assets	(3,140)	1,218	827
Accounts payable	(1,821)	(3,805)	3,615
Accrued expenses	(16,023)	7,862	4,844
Regulatory assets	(16,028)	(554)	12,372
Regulatory liabilities	(7,796)	25,534	(11,019)
Other noncurrent assets	(11,680)	(9,533)	(14,780)
Other noncurrent liabilities	(6,528)	(26,760)	7,387
Cash Provided by Operating Activities	296,720	381,985	322,738
INVESTING ACTIVITIES:
Property, plant, and equipment additions	(316,016)	(283,966)	(276,438)
Acquisitions	0	(18,504)	0
Proceeds from sale of assets	0	71	379
Investment in equity securities	(135)	(2,500)	0
Cash Used in Investing Activities	(316,151)	(304,899)	(276,059)
FINANCING ACTIVITIES:
Dividends on common stock	(115,127)	(109,202)	(101,270)
Proceeds from issuance of common stock, net	0	44,796	53,669
Line of credit borrowings, net	(19,000)	308,000	0
Issuance of long-term debt	150,000	0	250,000
Repayment of long-term debt	0	0	(250,000)
(Repayments) issuances of short-term borrowings, net	0	(319,556)	18,745
Treasury stock activity	1,432	2,249	1,083
Financing costs	(1,115)	(91)	(16,382)
Cash Provided by (Used In) Financing Activities	16,190	(73,804)	(44,155)
Net (Decrease) Increase in Cash, Cash Equivalents, and Restricted Cash	(3,241)	3,282	2,524
Cash, Cash Equivalents, and Restricted Cash, beginning of period	15,311	12,029	9,505
Cash, Cash Equivalents, and Restricted Cash, end of period	$ 12,070	$ 15,311	$ 12,029