Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Current assets:
Cash and cash equivalents	$ 8,755	$ 3,472	$ 20,854
Accounts receivable	31,512	66,236	30,778
Accrued unbilled revenue	13,995	62,381	13,896
Allowance for uncollectible accounts	(657)	(956)	(845)
Regulatory assets	41,092	45,781	37,504
Derivative instruments	2,044	1,735	1,530
Inventories	43,109	47,577	57,264
Gas reserves	16,579	15,704	16,072
Other current assets	11,672	24,949	13,028
Discontinued operations - current assets (Note 15)	12,743	3,057	1,923
Total current assets	180,844	269,936	192,004
Non-current assets:
Property, plant, and equipment	3,298,856	3,204,635	3,098,112
Less: Accumulated depreciation	984,998	960,477	942,558
Total property, plant, and equipment, net	2,313,858	2,244,158	2,155,554
Gas reserves	75,362	84,053	92,020
Regulatory assets	339,177	356,608	348,284
Derivative instruments	1,077	1,306	162
Other investments	64,854	66,363	68,885
Other non-current assets	11,588	6,505	3,164
Discontinued operations - non-current assets	0	10,817	205,081
Total non-current assets	2,805,916	2,769,810	2,873,150
Total assets	2,986,760	3,039,746	3,065,154
Current liabilities:
Short-term debt	47,100	54,200	0
Current maturities of long-term debt	74,785	96,703	61,991
Accounts payable	70,551	111,021	95,126
Taxes accrued	6,916	18,883	6,906
Interest accrued	6,652	6,773	5,966
Regulatory liabilities	34,275	34,013	28,041
Derivative instruments	11,744	18,722	4,734
Other current liabilities	32,935	39,942	31,015
Discontinued operations - current liabilities	12,922	1,593	1,303
Total current liabilities	297,880	381,850	235,082
Long-term debt	683,895	683,184	658,118
Deferred credits and other non-current liabilities:
Deferred tax liabilities	281,028	270,526	577,176
Regulatory liabilities	602,294	586,093	359,205
Pension and other postretirement benefit liabilities	218,061	223,333	219,718
Derivative instruments	3,913	4,649	3,466
Other non-current liabilities	140,163	135,292	134,793
Discontinued operations - non-current liabilities	0	12,043	12,167
Total deferred credits and other non-current liabilities	1,245,459	1,231,936	1,306,525
Commitments and contingencies (Note 14)
Equity:
Common stock - no par value; authorized 100,000 shares; issued and outstanding 28,800, 28,662, and 28,736 at June 30, 2018 and 2017, and December 31, 2017, respectively	452,195	448,865	444,058
Retained earnings	315,462	302,349	428,049
Accumulated other comprehensive loss	(8,131)	(8,438)	(6,678)
Total equity	759,526	742,776	865,429
Total liabilities and equity	$ 2,986,760	$ 3,039,746	$ 3,065,154