Significant Accounting Policies (Narrative) (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Significant Accounting Policies [Line Items]
Other investments	$ 3,300,000	$ 3,100,000
Accounts receivable	29,662,805	33,000,919
Fuel stock	10,773,773	6,321,676
ML&P For Fuel And South Central Power Project Costs [Member]
Significant Accounting Policies [Line Items]
Accounts receivable	1,300,000	1,400,000
BRU Operations For Gas Sales [Member]
Significant Accounting Policies [Line Items]
Accounts receivable	500,000	700,000
Funds On Deposit [Member]
Significant Accounting Policies [Line Items]
Restricted cash equivalents	$ 1,700,000	$ 1,700,000