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Fair Value of Derivative and Other Financial Instruments - Maturities of Debt Securities (Details) - PNMR and PNM $ in Thousands	Jun. 30, 2018 USD ($)
Available-for-Sale
Within 1 year	$ 8,883
After 1 year through 5 years	61,875
After 5 years through 10 years	67,445
After 10 years through 15 years	10,102
After 15 years through 20 years	9,574
After 20 years	43,241
Available-for-sale debt securities	$ 201,120

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- Definition

Available-for-sale Securities, Debt Maturities, after Fifteen Years Through Twenty Years, Fair Value

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