Related Party Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Deferred Purchased Power Costs		$ 5,200
Transmission costs deferred as regulatory liability		11,000
Operating revenues
Electric	$ 163,255	145,102	$ 136,917
Related Party Transaction, Utilities Operating Expense, Purchased Power net of deferred costs		430,666
Operating expenses
Purchased power	419,028	425,471	416,173
Transmission expense	54,070	43,876	42,460
Natural gas purchased for resale	45	90	97
Other operating expenses - paid to Xcel Energy Services Inc.	93,890	84,224	61,531
Interest expense	2	30	$ 22
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	71	31
Accounts payable	24,538	26,524
NSP-Minnesota
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	18,268	17,333
PSCo
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	71	22
SPS
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	71	31
Accounts payable	0	0
Other subsidiaries of Xcel Energy Inc.
Accounts Receivable and Payable with Affiliates [Abstract]
Accounts receivable	0	0
Accounts payable	$ 6,199	$ 9,169