Related Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating revenues
Electric	$ 136,917	$ 125,344	$ 124,334
Operating expenses
Purchased power	416,173	405,016	399,649
Transmission expense	42,460	44,942	40,870
Natural gas purchased for resale	97	116	98
Other operating expenses - paid to Xcel Energy Services Inc.	61,531	54,137	54,885
Interest expense	22	22	48
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	1,595	586
Accounts payable	24,986	31,556
NSP-Minnesota
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	18,584	26,632
PSCo
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	8	71
SPS
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	26	0
Accounts payable	0	4
Other subsidiaries of Xcel Energy Inc.
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	1,569	586
Accounts payable	$ 6,394	$ 4,849