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Segment Information - Schedule (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenues |  |  |  |  |  |  |  |  | $ 1,436,613 | $ 1,445,003 | $ 1,362,951
Utility margin |  |  |  |  |  |  |  |  | 1,036,887 | 1,037,524 | 982,355
Other operating expenses |  |  |  |  |  |  |  |  | 559,652 | 490,543 | 488,520
Depreciation and amortization |  |  |  |  |  |  |  |  | 241,188 | 231,942 | 209,110
Operating income | $ (17,404) | $ 127,990 | $ 79,329 | $ 46,132 | $ 22,936 | $ 142,484 | $ 85,105 | $ 55,960 | 236,047 | 315,039 | 284,725
Interest income |  |  |  |  |  |  |  |  | 15,540 | 15,916 | 22,293
Other income (deductions) |  |  |  |  |  |  |  |  | (15,286) | 22,429 | 16,789
Interest charges |  |  |  |  |  |  |  |  | (127,244) | (127,625) | (128,633)
Earnings before Income Taxes |  |  |  |  |  |  |  |  | 109,057 | 225,759 | 195,174
Income taxes (benefit) |  |  |  |  |  |  |  |  | 7,775 | 130,340 | 63,278
Net Earnings | (51,539) | 91,573 | 42,449 | 18,799 | (50,585) | 78,327 | 41,231 | 26,446 | 101,282 | 95,419 | 131,896
Valencia non-controlling interest |  |  |  |  |  |  |  |  | (15,112) | (15,017) | (14,519)
Subsidiary preferred stock dividends |  |  |  |  |  |  |  |  | (528) | (528) | (528)
Net Earnings Attributable to PNMR |  |  |  |  |  |  |  |  | 85,642 | 79,874 | 116,849
Total Assets | 6,865,551 |  |  |  | 6,646,103 |  |  |  | 6,865,551 | 6,646,103 | 6,471,080
Goodwill | 278,297 |  |  |  | 278,297 |  |  |  | 278,297 | 278,297 | 278,297
PNM |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Utility margin |  |  |  |  |  |  |  |  | 777,929 | 782,553 | 736,199
Other operating expenses |  |  |  |  |  |  |  |  | 481,030 | 414,457 | 407,922
Depreciation and amortization |  |  |  |  |  |  |  |  | 151,866 | 147,017 | 133,447
Operating income |  |  |  |  |  |  |  |  | 145,033 | 221,079 | 194,830
Interest income |  |  |  |  |  |  |  |  | 13,089 | 8,454 | 10,173
Other income (deductions) |  |  |  |  |  |  |  |  | (17,312) | 22,132 | 15,326
Interest charges |  |  |  |  |  |  |  |  | (76,458) | (82,697) | (87,469)
Earnings before Income Taxes |  |  |  |  |  |  |  |  | 64,352 | 168,968 | 132,860
Income taxes (benefit) |  |  |  |  |  |  |  |  | (5,971) | 81,555 | 40,922
Net Earnings |  |  |  |  |  |  |  |  | 70,323 | 87,413 | 91,938
Valencia non-controlling interest |  |  |  |  |  |  |  |  | (15,112) | (15,017) | (14,519)
Subsidiary preferred stock dividends |  |  |  |  |  |  |  |  | (528) | (528) | (528)
Net Earnings Attributable to PNMR |  |  |  |  |  |  |  |  | 54,683 | 71,868 | 76,891
Total Assets | 5,035,883 |  |  |  | 4,921,563 |  |  |  | 5,035,883 | 4,921,563 | 4,867,546
Goodwill | 51,632 |  |  |  | 51,632 |  |  |  | 51,632 | 51,632 | 51,632
TNMP |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Utility margin |  |  |  |  |  |  |  |  | 258,958 | 254,971 | 246,156
Other operating expenses |  |  |  |  |  |  |  |  | 96,272 | 98,221 | 93,389
Depreciation and amortization |  |  |  |  |  |  |  |  | 66,189 | 63,146 | 61,126
Operating income |  |  |  |  |  |  |  |  | 96,497 | 93,604 | 91,641
Interest income |  |  |  |  |  |  |  |  | 0 | 0 | 0
Other income (deductions) |  |  |  |  |  |  |  |  | 4,065 | 3,551 | 3,202
Interest charges |  |  |  |  |  |  |  |  | (32,091) | (30,084) | (29,335)
Earnings before Income Taxes |  |  |  |  |  |  |  |  | 68,471 | 67,071 | 65,508
Income taxes (benefit) |  |  |  |  |  |  |  |  | 16,880 | 31,512 | 23,836
Net Earnings |  |  |  |  |  |  |  |  | 51,591 | 35,559 | 41,672
Valencia non-controlling interest |  |  |  |  |  |  |  |  | 0 | 0 | 0
Subsidiary preferred stock dividends |  |  |  |  |  |  |  |  | 0 | 0 | 0
Net Earnings Attributable to PNMR |  |  |  |  |  |  |  |  | 51,591 | 35,559 | 41,672
Total Assets | 1,665,177 |  |  |  | 1,500,770 |  |  |  | 1,665,177 | 1,500,770 | 1,383,223
Goodwill | 226,665 |  |  |  | 226,665 |  |  |  | 226,665 | 226,665 | 226,665
Corporate and Other |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Utility margin |  |  |  |  |  |  |  |  | 0 | 0 | 0
Other operating expenses |  |  |  |  |  |  |  |  | (17,650) | (22,135) | (12,791)
Depreciation and amortization |  |  |  |  |  |  |  |  | 23,133 | 21,779 | 14,537
Operating income |  |  |  |  |  |  |  |  | (5,483) | 356 | (1,746)
Interest income |  |  |  |  |  |  |  |  | 2,451 | 7,462 | 12,120
Other income (deductions) |  |  |  |  |  |  |  |  | (2,039) | (3,254) | (1,739)
Interest charges |  |  |  |  |  |  |  |  | (18,695) | (14,844) | (11,829)
Earnings before Income Taxes |  |  |  |  |  |  |  |  | (23,766) | (10,280) | (3,194)
Income taxes (benefit) |  |  |  |  |  |  |  |  | (3,134) | 17,273 | (1,480)
Net Earnings |  |  |  |  |  |  |  |  | (20,632) | (27,553) | (1,714)
Valencia non-controlling interest |  |  |  |  |  |  |  |  | 0 | 0 | 0
Subsidiary preferred stock dividends |  |  |  |  |  |  |  |  | 0 | 0 | 0
Net Earnings Attributable to PNMR |  |  |  |  |  |  |  |  | (20,632) | (27,553) | (1,714)
Total Assets | 164,491 |  |  |  | 223,770 |  |  |  | 164,491 | 223,770 | 220,311
Goodwill | 0 |  |  |  | 0 |  |  |  | 0 | 0 | 0
Electricity |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenues | $ 343,756 | $ 422,666 | $ 352,313 | $ 317,878 | $ 332,605 | $ 419,900 | $ 362,320 | $ 330,178 | 1,436,613 | 1,445,003 | 1,362,951
Cost of energy |  |  |  |  |  |  |  |  | 399,726 | 407,479 | 380,596
Electricity | PNM |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenues |  |  |  |  |  |  |  |  | 1,091,965 | 1,104,230 | 1,035,913
Cost of energy |  |  |  |  |  |  |  |  | 314,036 | 321,677 | 299,714
Electricity | TNMP |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenues |  |  |  |  |  |  |  |  | 344,648 | 340,773 | 327,038
Cost of energy |  |  |  |  |  |  |  |  | 85,690 | 85,802 | 80,882
Electricity | Corporate and Other |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenues |  |  |  |  |  |  |  |  | 0 | 0 | 0
Cost of energy |  |  |  |  |  |  |  |  | $ 0 | $ 0 | $ 0

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