Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 7,289	$ 5,203	$ 9,838
Restricted cash	3,665	3,046	0
Accounts receivable (less allowances for doubtful accounts of $6,398, $4,052 and $5,518, respectively)	105,141	53,720	97,188
Accounts receivable — related parties	1,406	2,807	1,886
Accrued utility revenues	95,854	13,296	55,616
Inventories	49,717	53,309	39,693
Prepaid income taxes	1,977	7,711	2,013
Regulatory assets	605	8,338	1,635
Derivative instruments	678	1,354	7,077
Prepaid expenses & other current assets	23,066	16,406	26,131
Total current assets	289,398	165,190	241,077
Property, plant and equipment, at cost (less accumulated depreciation and amortization of $1,026,450, $1,010,781 and $987,850, respectively)	2,327,664	2,274,548	2,071,718
Goodwill	182,145	182,145	182,145
Regulatory assets	362,237	360,591	391,229
Other assets	13,249	11,541	12,354
Total assets	3,174,693	2,994,015	2,898,523
Current liabilities:
Current maturities of long-term debt	144,374	39,996	39,981
Short-term borrowings	181,500	170,000	98,400
Accounts payable	69,697	71,559	70,703
Accounts payable — related parties	13,420	6,890	11,385
Regulatory liabilities	17,091	12,988	25,830
Derivative instruments	2,244	1,071	295
Other current liabilities	106,177	110,978	113,468
Total current liabilities	534,503	413,482	360,062
Long-term debt	711,242	711,105	731,030
Deferred income taxes	340,772	635,465	566,519
Deferred investment tax credits	2,870	2,950	3,189
Pension and postretirement benefit obligations	140,224	143,674	181,809
Regulatory liabilities, Noncurrent	340,391	36,242	32,838
Other noncurrent liabilities	62,670	63,192	63,340
Total liabilities	2,132,672	2,006,110	1,938,787
Commitments and contingencies (Note 8)
Common stockholder’s equity:
Common Stock, $2.25 par value (authorized — 40,000,000 shares; issued and outstanding — 26,781,785 shares)	60,259	60,259	60,259
Additional paid-in capital	473,580	473,580	473,580
Retained earnings	534,161	480,857	456,781
Accumulated other comprehensive loss	(25,979)	(26,791)	(30,884)
Total common stockholder’s equity	1,042,021	987,905	959,736
Total liabilities and stockholder’s equity	$ 3,174,693	$ 2,994,015	$ 2,898,523