Capitalization (Details)	1 Months Ended
Jan. 31, 2017 USD ($)
First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Face Amount	$ 50,000,000
First Mortgage Bonds Due In 2042 [Member]
Debt Instrument [Line Items]
Face Amount	$ 10,000,000
Maturity Year	2042
Interest Rate	3.65%
First Mortgage Bonds Due In 2044 [Member]
Debt Instrument [Line Items]
Face Amount	$ 40,000,000
Maturity Year	2044
Interest Rate	3.69%

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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