Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Operating revenues	$ 91,239	$ 86,213	$ 479,441	$ 516,413
Operating expenses:
Cost of gas	25,538	27,239	175,697	223,855
Operations and maintenance	37,569	34,267	115,120	106,710
Environmental remediation	1,022	1,355	7,528	10,920
General taxes	7,589	7,540	24,792	23,423
Revenue taxes	3,522	0	20,731
Depreciation and amortization	21,485	20,352	63,507	60,529
Other operating expenses	625	0	2,157	0
Total operating expenses	97,350	90,753	409,532	425,437
Income (loss) from operations	(6,111)	(4,540)	69,909	90,976
Other income (expense), net	(312)	139	(1,139)	(624)
Interest expense, net	9,006	9,208	27,051	28,311
Income (loss) before income taxes	(15,429)	(13,609)	41,719	62,041
Income tax (benefit) expense	(4,285)	(5,722)	11,191	24,456
Net income (loss) from continuing operations	(11,144)	(7,887)	30,528	37,585
Loss from discontinued operations, net of tax,	(650)	(608)	(1,783)	(3,041)
Net income (loss)	(11,794)	(8,495)	28,745	34,544
Other comprehensive income:
Amortization of non-qualified employee benefit plan liability, net of taxes of $55 and $98 for the three months ended and $166 and $275 for the nine months ended September 30, 2018 and 2017, respectively	154	150	461	423
Comprehensive income (loss)	$ (11,640)	$ (8,345)	$ 29,206	$ 34,967
Average common shares outstanding:
Basic (in shares)	28,815	28,678	28,787	28,653
Diluted (in shares)	28,815	28,678	28,846	28,734
Earnings (loss) from continuing operations per share of common stock:
Basic (in dollars per share)	$ (0.39)	$ (0.28)	$ 1.06	$ 1.32
Diluted (in dollars per share)	(0.39)	(0.28)	1.06	1.31
Loss from discontinued operations per share of common stock:
Income (Loss) Per Basic Share from Discontinued Operation, Net of Tax	(0.02)	(0.02)	(0.06)	(0.11)
Income (Loss) Per Diluted Share from Discontinued Operation, Net of Tax	(0.02)	(0.02)	(0.06)	(0.11)
Earnings (loss) per share of common stock:
Basic (in dollars per share)	(0.41)	(0.30)	1.00	1.21
Diluted (in dollars per share)	$ (0.41)	$ (0.30)	$ 1.00	$ 1.20