Fair Value of Derivative and Other Financial Instruments, Debt Maturities (Details) (USD $) In Thousands	Sep. 30, 2011
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Available-for-sale debt securities, Within 1 year	$ 683
Available-for-sale debt securities, After 1 year through 5 years	20,259
Available-for-sale debt securities, After 5 years through 10 years	10,740
Available-for-sale debt securities, Over 10 years	39,705
Available-for-sale debt securities	71,387
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Held-to-maturity debt securities, Due within 1 year	0
Held-to-maturity debt securities, After 1 year through 5 years	123,206
Held-to-maturity debt securities, After 5 years through 10 years	3,370
Held-to-maturity debt securities, Over 10 years	0
Held-to-maturity debt securities	126,576
Public Service Company of New Mexico [Member]
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Held-to-maturity debt securities, Due within 1 year	0
Held-to-maturity debt securities, After 1 year through 5 years	112,083
Held-to-maturity debt securities, After 5 years through 10 years	0
Held-to-maturity debt securities, Over 10 years	0
Held-to-maturity debt securities	$ 112,083

This item represents the fair value of debt securities which are expected to mature after five years and through ten years from the balance sheet date and which are categorized neither as held-to-maturity nor trading securities.

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For an unclassified balance sheet, total of debt securities categorized neither as held-to-maturity nor trading.

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This item represents the total of all debt securities grouped by maturity dates, at fair value, which are categorized as held-to-maturity.

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