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Segment financial information (Details) $ in Thousands |  |  |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Feb. 02, 2018 MWh MW | Dec. 26, 2017 USD ($) | Nov. 24, 2017 MW | Dec. 31, 2017 USD ($) | Sep. 30, 2017 USD ($) | Jun. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Sep. 30, 2016 USD ($) | Jun. 30, 2016 USD ($) | Mar. 31, 2016 USD ($) | Dec. 31, 2017 USD ($) MW | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  | $ 658,597 | $ 673,185 | $ 632,281 | $ 591,562 | $ 617,395 | $ 646,055 | $ 566,244 | $ 550,960 | $ 2,555,625 | $ 2,380,654 | $ 2,602,982
Depreciation and amortization |  |  |  |  |  |  |  |  |  |  |  | 221,998 | 204,746 | 195,585
Interest expense, net |  |  |  |  |  |  |  |  |  |  |  | 91,128 | 88,558 | 88,476
Income (loss) before income taxes |  |  |  |  |  |  |  |  |  |  |  | 276,580 | 373,841 | 254,788
Income taxes (benefit) |  |  |  |  |  |  |  |  |  |  |  | 109,393 | 123,695 | 93,021
Net income (loss) |  |  |  | 32,843 | 60,544 | 39,134 | 34,666 | 45,107 | 127,613 | 44,601 | 32,825 | 167,187 | 250,146 | 161,767
Preferred stock dividends of subsidiaries |  |  |  |  |  |  |  |  |  |  |  | 1,890 | 1,890 | 1,890
Net income for common stock |  |  |  | 32,370 | $ 60,073 | $ 38,661 | $ 34,193 | 44,634 | $ 127,142 | $ 44,128 | $ 32,352 | 165,297 | 248,256 | 159,877
Capital expenditures |  |  |  |  |  |  |  |  |  |  |  | 495,187 | 330,043 | 363,804
Assets |  |  |  | 13,099,828 |  |  |  | 12,425,506 |  |  |  | 13,099,828 | 12,425,506 | 11,782,018
Electric utility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  |  |  | 2,257,566 | 2,094,368 | 2,335,166
Depreciation and amortization |  |  |  |  |  |  |  |  |  |  |  | 201,282 | 193,996 | 186,319
Interest expense, net |  |  |  |  |  |  |  |  |  |  |  | 69,637 | 66,824 | 66,370
Income (loss) before income taxes |  |  |  |  |  |  |  |  |  |  |  | 205,145 | 229,113 | 217,131
Income taxes (benefit) |  |  |  |  |  |  |  |  |  |  |  | 83,199 | 84,801 | 79,422
Net income (loss) |  |  |  |  |  |  |  |  |  |  |  | 121,946 | 144,312 | 137,709
Preferred stock dividends of subsidiaries |  |  |  |  |  |  |  |  |  |  |  | 1,995 | 1,995 | 1,995
Net income for common stock |  |  |  |  |  |  |  |  |  |  |  | 119,951 | 142,317 | 135,714
Capital expenditures |  |  |  |  |  |  |  |  |  |  |  | 441,598 | 320,437 | 350,161
Assets |  |  |  | 6,196,281 |  |  |  | 5,975,428 |  |  |  | 6,196,281 | 5,975,428 | 5,672,210
Bank |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  |  |  | 297,640 | 285,924 | 267,733
Depreciation and amortization |  |  |  |  |  |  |  |  |  |  |  | 19,416 | 9,813 | 7,928
Interest expense, net |  |  |  |  |  |  |  |  |  |  |  | 12,156 | 12,755 | 11,326
Income (loss) before income taxes |  |  |  |  |  |  |  |  |  |  |  | 98,716 | 87,352 | 83,812
Income taxes (benefit) |  |  |  |  |  |  |  |  |  |  |  | 31,719 | 30,073 | 29,082
Net income (loss) |  |  |  |  |  |  |  |  |  |  |  | 66,997 | 57,279 | 54,730
Preferred stock dividends of subsidiaries |  |  |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Net income for common stock |  |  |  |  |  |  |  |  |  |  |  | 66,997 | 57,279 | 54,730
Capital expenditures |  |  |  |  |  |  |  |  |  |  |  | 53,272 | 9,394 | 13,470
Assets |  |  |  | 6,798,659 |  |  |  | 6,421,357 |  |  |  | 6,798,659 | 6,421,357 | 6,014,755
Other |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  |  |  | 419 | 362 | 83
Depreciation and amortization |  |  |  |  |  |  |  |  |  |  |  | 1,300 | 937 | 1,338
Interest expense, net |  |  |  |  |  |  |  |  |  |  |  | 9,335 | 8,979 | 10,780
Income (loss) before income taxes |  |  |  |  |  |  |  |  |  |  |  | (27,281) | 57,376 | (46,155)
Income taxes (benefit) |  |  |  |  |  |  |  |  |  |  |  | (5,525) | 8,821 | (15,483)
Net income (loss) |  |  |  |  |  |  |  |  |  |  |  | (21,756) | 48,555 | (30,672)
Preferred stock dividends of subsidiaries |  |  |  |  |  |  |  |  |  |  |  | (105) | (105) | (105)
Net income for common stock |  |  |  |  |  |  |  |  |  |  |  | (21,651) | 48,660 | (30,567)
Capital expenditures |  |  |  |  |  |  |  |  |  |  |  | 317 | 212 | 173
Assets |  |  |  | $ 104,888 |  |  |  | $ 28,721 |  |  |  | 104,888 | 28,721 | 95,053
Operating Segments |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  |  |  | 2,555,625 | 2,380,654 | 2,602,982
Operating Segments | Electric utility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  |  |  | 2,257,455 | 2,094,224 | 2,335,135
Operating Segments | Bank |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  |  |  | 297,640 | 285,924 | 267,733
Operating Segments | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  |  |  | 530 | 506 | 114
Intersegment eliminations |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Intersegment eliminations | Electric utility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  |  |  | 111 | 144 | 31
Intersegment eliminations | Bank |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Intersegment eliminations | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  |  |  | $ (111) | $ (144) | $ (31)
Hamakua Energy Partners, L.P. (HEP) |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Power produced by power plants (in megawatts) | MW |  |  | 60 |  |  |  |  |  |  |  |  | 60 |  |
Hamakua Energy Partners, L.P. (HEP) | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of secured notes |  | $ 67,000 |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, stated interest rate |  |  |  | 4.02% |  |  |  |  |  |  |  | 4.02% |  |
Mauo, LLC | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment financial information |  |  |  |  |  |  |  |  |  |  |  |  |  |
Power produced by power plants (in megawatts) | MW | 8.6 |  |  |  |  |  |  |  |  |  |  |  |  |
Power storage capacity (in megawatt hours) | MWh | 42.3 |  |  |  |  |  |  |  |  |  |  |  |  |
Power purchase agreement term | 15 years |  |  |  |  |  |  |  |  |  |  |  |  |
Power purchase agreement extension term | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |

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