Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	$ 1,209	$ 1,397	$ 1,466
Charged to costs and expenses	2,619	2,885	3,358
Charged to other accounts	0	0	0
Write-offs	2,747	3,073	3,427
Balance at end of year	1,081	1,209	1,397
Public Service Company of New Mexico
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	1,209	1,397	1,466
Charged to costs and expenses	2,615	2,871	3,344
Charged to other accounts	0	0	0
Write-offs	2,743	3,059	3,413
Balance at end of year	1,081	1,209	1,397
Texas-New Mexico Power Company
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	0	0	0
Charged to costs and expenses	4	14	14
Charged to other accounts	0	0	0
Write-offs	4	14	14
Balance at end of year	$ 0	$ 0	$ 0