Summary of Accounting Policies Summary of Effect of Adoption on Consolidated Financial Statements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Item Effected [Line Items]
Accrued revenue	$ 12,352		$ 12,352		$ 22,279
Regulated Energy Operating Revenue	72,770	$ 69,703	252,667	$ 238,353
Regulated Energy cost of sales	21,501	22,794	89,741	87,206
Depreciation and amortization	10,633	9,362	30,176	27,267
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	7,595	11,157	53,510	52,804
Income taxes	2,057	4,324	14,731	20,781
Net Income	5,538	$ 6,833	38,779	$ 32,023	58,124
Other assets	5,293		5,293		3,699
Retained earnings	249,805		249,805		$ 229,141
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Item Effected [Line Items]
Accrued revenue	13,658		13,658
Regulated Energy Operating Revenue	72,879		253,659
Regulated Energy cost of sales	21,512		90,454
Depreciation and amortization	10,629		30,150
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	7,697		53,815
Income taxes	2,086		14,819
Net Income	5,611		38,996
Other assets	5,702		5,702
Retained earnings	251,520		251,520
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Item Effected [Line Items]
Accrued revenue	(1,306)		(1,306)
Deferred Revenue, Period Increase (Decrease)	(109)		(992)
Regulated Energy cost of sales	(11)		(713)
Depreciation and amortization	4		26
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(102)		(305)
Income taxes	(29)		(88)
Net Income	(73)		(217)
Other assets	(409)		(409)
Retained earnings	$ (1,715)		$ (1,715)