The percentage of undivided interest in property, plant and equipment.

No definition available.

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- Definition

Amount of liability for consideration received or receivable from customer which is not included in transaction price, when consideration is expected to be refunded to customer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 55
-Paragraph 25
-URI http://asc.fasb.org/extlink&oid=96862333&loc=SL49130609-203046-203046

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 55
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=96862333&loc=SL49130607-203046-203046

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 32
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=82859839&loc=SL51751984-203043

+ Details

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Balance Type:	credit
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- Definition

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.

+ References

No definition available.

+ Details

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Balance Type:	na
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- Definition

Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

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

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

+ Details

Name:	us-gaap_RegulatoryAssetsNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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- Details

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- Details

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- Details

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- Details

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Summary of significant accounting policies: - Recently issued or adopted accounting pronouncements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Jan. 01, 2019	Dec. 31, 2017
Recently Issued or Adopted Accounting Pronouncements
Regulatory assets	$ 655,063,000		$ 585,084,000
Refund liability	30,870,000		29,149,000
ASU 2014-09
Recently Issued or Adopted Accounting Pronouncements
Refund liability	30,870,000		29,149,000
ASU 2016-01
Recently Issued or Adopted Accounting Pronouncements
Regulatory assets	$ 975,000		$ 618,000
ASU 2016-02 \| Scherer Unit No. 2
Recently Issued or Adopted Accounting Pronouncements
Percentage of undivided interest	60.00%
ASU 2016-02 \| Adjustments
Recently Issued or Adopted Accounting Pronouncements
Lease assets		$ 6,983,000
Lease liabilities		$ 6,983,000