Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Current assets:
Cash and cash equivalents	$ 11,215	$ 3,472	$ 40,639
Accounts receivable	78,091	68,362	70,429
Accrued unbilled revenue	38,752	62,381	38,017
Allowance for uncollectible accounts	(1,113)	(956)	(1,668)
Regulatory assets	45,900	45,781	34,874
Derivative instruments	1,130	1,735	2,908
Inventories	35,135	47,973	48,484
Gas reserves	15,124	15,704	15,378
Other current assets	17,460	25,484	16,832
Total current assets	241,694	269,936	265,893
Non-current assets:
Property, plant, and equipment	3,261,886	3,215,451	3,247,177
Less: Accumulated depreciation	972,776	960,477	960,336
Total property, plant, and equipment, net	2,289,110	2,254,974	2,286,841
Gas reserves	80,560	84,053	96,630
Regulatory assets	343,037	356,608	349,057
Derivative instruments	1,148	1,306	46
Other investments	66,709	66,363	68,729
Other non-current assets	7,081	6,506	3,460
Total non-current assets	2,787,645	2,769,810	2,804,763
Total assets	3,029,339	3,039,746	3,070,656
Current liabilities:
Short-term debt	50,000	54,200	0
Current maturities of long-term debt	74,785	96,703	61,994
Accounts payable	78,321	112,308	73,245
Taxes accrued	12,352	18,883	16,653
Interest accrued	9,262	6,773	10,581
Regulatory liabilities	34,946	34,013	33,211
Derivative instruments	17,607	18,722	1,638
Other current liabilities	39,580	40,248	37,697
Total current liabilities	316,853	381,850	235,019
Long-term debt	683,497	683,184	657,716
Deferred credits and other non-current liabilities:
Deferred tax liabilities	283,129	270,526	575,451
Regulatory liabilities	600,442	586,093	357,587
Pension and other postretirement benefit liabilities	221,732	223,333	223,253
Derivative instruments	2,355	4,649	2,546
Other non-current liabilities	149,126	147,335	144,469
Total deferred credits and other non-current liabilities	1,256,784	1,231,936	1,303,306
Commitments and contingencies (see Note 14)
Equity:
Common stock - no par value; authorized 100,000 shares; issued and outstanding 28,781, 28,644, and 28,736 at March 31, 2018 and 2017, and December 31, 2017, respectively	450,408	448,865	442,647
Retained earnings	330,081	302,349	438,783
Accumulated other comprehensive loss	(8,284)	(8,438)	(6,815)
Total equity	772,205	742,776	874,615
Total liabilities and equity	$ 3,029,339	$ 3,039,746	$ 3,070,656

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

Name:	us-gaap_AccountsPayableCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business.