Related Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating revenues [Abstract]
Electric	$ 6,539	$ 7,187	$ 6,805
Operating expenses [Abstract]
Purchased power	9,271	10,896	9,428
Other operating expenses - paid to Xcel Energy Services Inc.	117,277	118,370	109,111
Interest expense	76	83	90
Interest income	10	1	25
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	4,791	1,314
Accounts payable	12,363	11,828
NSP Minnesota [Member]
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	3,820	1,314
Accounts payable	0	0
NSP-Wisconsin [Member]
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	4	0
Accounts payable	0	0
PSCo [Member]
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	69	319
Other Subsidiaries of Xcel Energy Inc. [Member]
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	967	0
Accounts payable	$ 12,294	$ 11,509