Commitments Disclosure [Line Items]

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- Definition

Litigation Settlement, Fair Value of Property Condemned

+ References

No definition available.

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- Definition

Loss Contingency, Punitive Damages Sought, Value

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No definition available.

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- Definition

Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments.

+ References

No definition available.

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- Definition

Amount of contractual obligation due after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

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- Definition

Amount of contractual obligation due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

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- Definition

Amount of contractual obligation due in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

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- Definition

Amount of contractual obligation due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

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- Definition

Amount of contractual obligation due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

+ Details

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- Definition

Amount of contractual obligation due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

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- Definition

Amount of gain (loss) recognized in settlement of litigation and insurance claims. Excludes claims within an insurance entity's normal claims settlement process.

+ References

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- Definition

Amount awarded from other party in judgment or settlement of litigation.

+ References

No definition available.

+ Details

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- Definition

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14557-108349

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

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Commitments and contingencies - Estimates of Future Commitments (Detail) - USD ($) $ in Thousands				12 Months Ended
	Oct. 30, 2018	Jun. 22, 2017	May 06, 2014	Dec. 31, 2018
Commitments Disclosure [Line Items]
Year 1				$ 243,130
Year 2				110,155
Year 3				84,529
Year 4				87,629
Year 5				81,503
Thereafter				730,663
Total				1,337,609
Power purchase
Commitments Disclosure [Line Items]
Year 1				46,536
Year 2				10,896
Year 3				11,114
Year 4				11,338
Year 5				11,566
Thereafter				191,208
Total				282,658
Gas supply and service agreements
Commitments Disclosure [Line Items]
Year 1				77,658
Year 2				51,349
Year 3				27,672
Year 4				24,422
Year 5				22,424
Thereafter				48,313
Total				251,838
Service agreements
Commitments Disclosure [Line Items]
Year 1				43,732
Year 2				39,093
Year 3				38,451
Year 4				37,463
Year 5				40,737
Thereafter				312,559
Total				512,035
Capital projects
Commitments Disclosure [Line Items]
Year 1				67,575
Year 2				1,663
Year 3				196
Year 4				7,330
Year 5				0
Thereafter				0
Total				76,764
Operating leases
Commitments Disclosure [Line Items]
Year 1				7,629
Year 2				7,154
Year 3				7,096
Year 4				7,076
Year 5				6,776
Thereafter				178,583
Total				214,314
Gaia Power Inc. vs APUC
Commitments Disclosure [Line Items]
Damages claimed by other party in lawsuit	$ 345,000
Punitive damages claimed by other party in lawsuit	$ 25,000
Lawsuit vs. Mountain Water Company and City of Missoula
Commitments Disclosure [Line Items]
Fair value of condemned property			$ 88,600
Litigation settlement, amount		$ 83,863
Gain on long-lived assets				$ 4,370