Acquisitions - Additional Information (Details)
$ in Thousands |
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|
3 Months Ended |
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Mar. 07, 2018
USD ($)
MW
|
Apr. 21, 2017
USD ($)
kV
mi
MW
|
Jun. 30, 2018
USD ($)
|
Dec. 31, 2017
USD ($)
|
Jun. 30, 2017
USD ($)
|
| Business Acquisition [Line Items] |
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| Liabilities assumed |
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|
$ 352,570
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|
$ 148,456
|
| Long-term debt, gross |
|
|
2,224,704
|
$ 1,967,627
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|
| Tsugaru Holdings [Member] |
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| Business Acquisition [Line Items] |
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| Consideration |
$ 282,548
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| Cash Consideration |
176,600
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| Contingent Consideration |
105,900
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|
|
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| Liabilities assumed |
181,300
|
|
|
|
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| Transaction costs |
|
|
1,300
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| Decrease in property, plant and equipment |
|
|
600
|
|
|
| Decrease in construction in progress |
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|
$ 600
|
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| Debt Assumed |
181,300
|
|
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| Tsugaru Holdings [Member] | Term Conversion Of Tsugaru Construction Loan [Member] |
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| Business Acquisition [Line Items] |
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|
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| Contingent Consideration |
102,900
|
|
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| Tsugaru Holdings [Member] | Term Conversion Of Ohorayama Construction Loan [Member] |
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| Business Acquisition [Line Items] |
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| Contingent Consideration |
$ 3,000
|
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| Broadview Project [Member] |
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| Business Acquisition [Line Items] |
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| Cash Consideration |
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$ 214,700
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| Contingent Consideration |
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$ 21,300
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| Percentage of voting interests acquired |
|
100.00%
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|
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| Consideration transferred, liabilities incurred |
|
$ 2,400
|
|
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| Debt Assumed |
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$ 51,200
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| Broadview Holdings' Interest in Broadview [Member] |
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| Business Acquisition [Line Items] |
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| Ownership percentage |
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100.00%
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| Tsugaru [Member] | Aomori Prefecture, Japan [Member] | Tsugaru Holdings [Member] |
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| Business Acquisition [Line Items] |
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| Generating capacity | MW |
122
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| Ohorayama [Member] | Kochi Prefecture, Japan [Member] | Tsugaru Holdings [Member] |
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| Business Acquisition [Line Items] |
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| Generating capacity | MW |
33
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| Kanagi [Member] | Shimane Prefecture, Japan [Member] | Tsugaru Holdings [Member] |
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| Business Acquisition [Line Items] |
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| Generating capacity | MW |
10
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| Otsuki [Member] | Kochi Prefecture, Japan [Member] | Tsugaru Holdings [Member] |
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| Business Acquisition [Line Items] |
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| Generating capacity | MW |
12
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| Futtsu [Member] | Chiba Prefecture, Japan [Member] | Tsugaru Holdings [Member] |
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| Business Acquisition [Line Items] |
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| Generating capacity | MW |
29
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| Class B membership interest in Broadview Holdings [Member] |
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| Business Acquisition [Line Items] |
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| Ownership percentage |
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100.00%
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| Western Interconnect [Member] |
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| Business Acquisition [Line Items] |
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| Ownership percentage |
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99.00%
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| Initial distributable cash flow from Broadview [Member] |
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| Business Acquisition [Line Items] |
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| Ownership percentage |
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84.00%
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| Broadview [Member] |
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| Business Acquisition [Line Items] |
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| Generating capacity | MW |
|
324
|
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| Western Interconnect [Member] |
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| Business Acquisition [Line Items] |
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| Transmission line length | mi |
|
35
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| Transmission-level voltage | kV |
|
345
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| Long-term debt, gross |
|
$ 54,400
|
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