CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
OPERATING ACTIVITIES:
Net Income	$ 164,172	$ 151,209	$ 120,686
Items not affecting cash:
Depreciation and depletion	159,336	144,702	123,776
Amortization of debt issue costs, discount and deferred hedge gain	2,117	2,258	5,033
Stock-based compensation costs	6,731	5,082	3,262
Equity portion of allowance for funds used during construction	(4,589)	(8,684)	(6,554)
Gain on disposition of assets	(15)	(20)	(1,330)
Deferred income taxes	(8,184)	33,886	(9,612)
Changes in current assets and liabilities:
Restricted cash	2,208	6,920	(6,408)
Accounts receivable	(5,146)	9,069	12,622
Inventories	4,252	1,636	747
Other current assets	(2,384)	5,514	4,201
Accounts payable	3,639	(11,169)	(9,565)
Accrued expenses	25,124	(22,738)	8,530
Regulatory assets	1,871	(3,974)	(8,952)
Regulatory liabilities	(54,629)	24,821	9,763
Other noncurrent assets	(7,311)	(5,584)	2,853
Other noncurrent liabilities	1,820	6,890	987
Cash Provided by Operating Activities	289,012	339,818	250,039
INVESTING ACTIVITIES:
Property, plant, and equipment additions	(287,901)	(283,705)	(270,384)
Acquisitions	0	(146,668)	(903,573)
Proceeds from sale of assets	1,354	30,209	1,535
Change in restricted cash	0	16,108	(16,358)
Investment in New Market Tax Credit program	0	0	(18,169)
Cash Used in Investing Activities	(286,547)	(384,056)	(1,206,949)
FINANCING ACTIVITIES:
Dividends on common stock	(95,765)	(90,058)	(65,019)
Proceeds from issuance of common stock, net	0	56,651	399,207
Issuance of long-term debt	249,660	270,000	505,789
Repayment of long-term debt	(225,205)	(150,025)	(90)
Issuances (repayments) of short-term borrowings, net	70,937	(37,966)	126,890
Treasury stock activity	(561)	(664)	(814)
Financing costs	(8,432)	(12,082)	(5,248)
Cash (Used In) Provided by Financing Activities	(9,366)	35,856	960,715
Net (Decrease) Increase in Cash and Cash Equivalents	(6,901)	(8,382)	3,805
Cash and Cash Equivalents, beginning of period	11,980	20,362	16,557
Cash and Cash Equivalents, end of period	$ 5,079	$ 11,980	$ 20,362