Debt (Schedule Of Debt Issuance Costs Associated With Long-Term Obligations) (Details) - USD ($)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term Obligations	$ 470,442,665	$ 473,024,497
Less current installments	24,836,667	24,115,980
Less unnamortized debt issuance costs	2,715,745	2,680,897
Total long-term obligations, excluding current installments	442,890,253	446,227,620
2011 CoBank Note [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Long-term Obligations	$ 0	$ 24,941,165
Variable interest rate	2.78%	2.78%
Maturity year	2003
2011 Series A Bond Of 4.20% Maturing 2031 [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Long-term Obligations	$ 67,500,000	$ 72,000,000
Interest rate	4.20%	4.20%
Maturity year	2031
2011 Series A Bond Of 4.75% Maturing 2041 [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Long-term Obligations	$ 154,166,665	$ 160,333,332
Interest rate	4.75%	4.75%
Maturity year	2041
2012 Series A Bond Of 4.01% Maturing 2032 [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Long-term Obligations	$ 60,000,000	$ 63,750,000
Interest rate	4.01%	4.01%
Maturity year	2032
2012 Series A Bond Of 4.41% Maturing 2042 [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Long-term Obligations	$ 95,000,000	$ 102,000,000
Interest rate	4.41%	4.41%
Maturity year	2042
2012 Series A Bond Of 4.78% Maturing 2042 [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Long-term Obligations	$ 50,000,000	$ 50,000,000
Interest rate	4.78%	4.78%
Maturity year	2042
2016 CoBank Note [Member]
Debt Instrument [Line Items]
Long-term Obligations	$ 43,776,000	$ 0
Interest rate	2.58%	2.58%
Maturity year	2031

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Description of the maturity date of the debt instrument including whether the debt matures serially and, if so, a brief description of the serial maturities.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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