Consolidated Balance Sheets (Unaudited) - USD ($)	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Current assets:
Cash and cash equivalents	$ 20,854,000	$ 3,521,000	$ 5,463,000
Accounts receivable	31,908,000	66,700,000	23,353,000
Accrued unbilled revenue	13,896,000	64,946,000	14,175,000
Allowance for uncollectible accounts	(845,000)	(1,290,000)	(570,000)
Regulatory assets	37,504,000	42,362,000	49,004,000
Derivative instruments	1,530,000	17,031,000	7,445,000
Inventories	57,666,000	54,129,000	66,171,000
Gas reserves	16,072,000	15,926,000	15,707,000
Other current assets	13,419,000	24,728,000	21,312,000
Total current assets	192,004,000	288,053,000	202,060,000
Non-current assets:
Property, plant, and equipment	3,333,668,000	3,208,816,000	3,146,631,000
Less: Accumulated depreciation	973,084,000	947,916,000	932,179,000
Total property, plant, and equipment, net	2,360,584,000	2,260,900,000	2,214,452,000
Gas reserves	92,020,000	100,184,000	108,286,000
Regulatory assets	348,284,000	357,530,000	344,969,000
Derivative instruments	162,000	3,265,000	3,541,000
Other investments	68,885,000	68,376,000	67,868,000
Other non-current assets	3,215,000	1,493,000	1,968,000
Total non-current assets	2,873,150,000	2,791,748,000	2,741,084,000
Total assets	3,065,154,000	3,079,801,000	2,943,144,000
Current liabilities:
Short-term debt	0	53,300,000	152,800,000
Current maturities of long-term debt	61,991,000	39,989,000	24,987,000
Accounts payable	95,761,000	85,664,000	57,756,000
Taxes accrued	6,906,000	12,149,000	6,237,000
Interest accrued	5,966,000	5,966,000	5,793,000
Regulatory liabilities	28,041,000	40,290,000	27,300,000
Derivative instruments	4,734,000	1,315,000	3,471,000
Other current liabilities	31,683,000	35,844,000	35,289,000
Total current liabilities	235,082,000	274,517,000	313,633,000
Long-term debt	658,118,000	679,334,000	570,045,000
Deferred credits and other non-current liabilities:
Deferred tax liabilities	577,176,000	557,085,000	554,400,000
Regulatory liabilities	359,205,000	349,319,000	341,259,000
Pension and other postretirement benefit liabilities	219,718,000	225,725,000	219,049,000
Derivative instruments	3,466,000	913,000	474,000
Other non-current liabilities	146,960,000	142,411,000	144,285,000
Total deferred credits and other non-current liabilities	1,306,525,000	1,275,453,000	1,259,467,000
Commitments and contingencies (see Note 13)
Equity:
Common stock - no par value; authorized 100,000 shares; issued and outstanding 28,662, 27,550, and 28,630 at June 30, 2017 and 2016, and December 31, 2016, respectively	444,058,000	445,187,000	388,967,000
Retained earnings	428,049,000	412,261,000	417,857,000
Accumulated other comprehensive loss	(6,678,000)	(6,951,000)	(6,825,000)
Total equity	865,429,000	850,497,000	799,999,000
Total liabilities and equity	$ 3,065,154,000	$ 3,079,801,000	$ 2,943,144,000