Fair Value of Financial Assets and Liabilities, Derivative Assets and Liabilities at Fair Value (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 0
Derivative Liability, Fair Value, Gross Liability	0
Prepayments and other	4,531,000	5,056,000
Fair Value Measured on a Recurring Basis [Member] | Other Current Assets [Member] | Natural Gas Commodity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset		580,000	[1]
Fair Value Measured on a Recurring Basis [Member] | Level 1 [Member] | Other Current Assets [Member] | Natural Gas Commodity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset		0
Fair Value Measured on a Recurring Basis [Member] | Level 2 [Member] | Other Current Assets [Member] | Natural Gas Commodity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset		580,000
Fair Value Measured on a Recurring Basis [Member] | Level 3 [Member] | Other Current Assets [Member] | Natural Gas Commodity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset		0
Fair Value Measured on a Recurring Basis [Member] | Fair Value Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepayments and other		5,100,000
Fair Value Measured on a Recurring Basis [Member] | Fair Value Total [Member] | Other Current Assets [Member] | Natural Gas Commodity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset		580,000
Fair Value Measured on a Recurring Basis [Member] | Counterparty Netting [Member] | Other Current Assets [Member] | Natural Gas Commodity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset		$ 0	[2]

[1] Included in other current assets balance of $5.1 million at Dec. 31, 2013 in the consolidated balance sheets.

[2] NSP-Wisconsin nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2013. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.