Related Party Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Deferred Purchased Power Costs			$ 5,200
Transmission costs deferred as regulatory liability			11,000
Operating revenues
Electric	$ 170,483	$ 163,255	145,102
Operating expenses
Purchased power	413,615	419,028	430,666
Transmission expense	61,920	54,070	43,876
Natural gas purchased for resale	41	45	90
Other operating expenses - paid to Xcel Energy Services Inc.	106,454	93,890	84,224
Interest expense	4	2	$ 30
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	333	71
Accounts payable	29,037	24,538
NSP-Minnesota
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	18,567	18,268
PSCo
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	974	71
SPS
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	333	71
Accounts payable	0	0
Other subsidiaries of Xcel Energy Inc.
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	$ 9,496	$ 6,199