Income Taxes (Details)	1 Months Ended	3 Months Ended	12 Months Ended
	Aug. 31, 2016	Sep. 30, 2015	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2012	Dec. 31, 2016 USD ($) $ / kWh	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Consolidated Appropriations Act of 2016 [Abstract]
Excise Tax Delay			2 years
Earliest Open Tax Year Subject To Examination			2012
Unrecognized Tax Benefits [Abstract]
Unrecognized Tax Benefits - Permanent tax positions							$ 400,000	$ 200,000
Unrecognized tax benefit — Temporary tax positions							4,900,000	4,300,000
Total unrecognized tax benefit			$ 4,500,000	$ 3,000,000	$ 1,500,000		5,300,000	4,500,000	$ 3,000,000
Tax Increase Prevention Act of 2014 [Abstract]
Number of years bonus depreciation was extended				1 year
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at Jan. 1			4,500,000	$ 3,000,000	1,500,000
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions			500,000	1,900,000	1,900,000
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions			0	(300,000)	(200,000)
Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions			500,000	800,000	100,000
Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions			(200,000)	(900,000)	(200,000)
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities			0	0	(100,000)
Balance at Dec. 31			$ 5,300,000	$ 4,500,000	$ 3,000,000
Tax Benefits Associated With NOL And Tax Credit Carryforwards [Abstract]
NOL and tax credit carryforwards							(1,200,000)	(900,000)
Decrease in Unrecognized Tax Benefits is Reasonably Possible							2,000,000
Amounts accrued for penalties related to unrecognized tax benefits							0	0	$ 0
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			35.00%	35.00%	35.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent			4.90%	4.80%	4.90%
Effective Income Tax Rate Reconciliation Change In Unrecognized Tax Benefits, Percent			0.10%	0.10%	0.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Percent			(0.70%)	(0.70%)	(0.70%)
Effective Income Tax Rate Reconciliation Regulatory Differences Utility Plant Items, Percent			(0.70%)	(1.70%)	(1.60%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent			(0.30%)	(0.30%)	(0.10%)
Effective Income Tax Rate Reconciliation, Percent			38.30%	37.20%	37.50%
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)			$ 5,367,000	$ (4,715,000)	$ (3,932,000)
Current State and Local Tax Expense (Benefit)			131,000	2,150,000	453,000
Current Change In Unrecognized Tax Expense (Benefit)			559,000	1,498,000	1,013,000
Deferred Federal Income Tax Expense (Benefit)			29,588,000	40,580,000	38,321,000
Deferred State and Local Income Tax Expense (Benefit)			8,212,000	6,675,000	8,042,000
Deferred Change In Unrecognized Tax Expense (Benefit)			(432,000)	(1,422,000)	(967,000)
Deferred investment tax credits			(523,000)	(528,000)	(527,000)
Income Tax Expense (Benefit)			42,902,000	44,238,000	42,403,000
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred tax expense (benefit) excluding selected items			39,530,000	51,084,000	49,793,000
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities			(2,112,000)	(5,200,000)	(4,346,000)
Other Comprehensive Income (Loss), Tax			(50,000)	(51,000)	(51,000)
Deferred Income Tax Expense (Benefit)			37,368,000	$ 45,833,000	$ 45,396,000
Deferred Tax Liabilities, Gross [Abstract]
Deferred Tax Liabilities, Property, Plant and Equipment							412,071,000	382,592,000
Deferred Tax Liabilities, Regulatory Assets							75,392,000	78,233,000
Deferred Tax Liabilities, Compensation and Benefits, Employee Benefits							15,443,000	18,028,000
Deferred Tax Liabilities, Other							9,949,000	10,190,000
Deferred Tax Liabilities, Gross							512,855,000	489,043,000
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets, Operating Loss Carryforwards							35,216,000	37,508,000
Deferred Tax Assets Environmental Remediation							25,842,000	37,938,000
Deferred Tax Assets Regulatory Liabilities							5,779,000	9,328,000
Deferred Tax Assets Deferred Investment Tax Credits							4,996,000	5,312,000
Deferred Tax Assets Tax credit carryforward							3,704,000	4,760,000
Deferred Tax Assets, Other							6,725,000	3,134,000
Deferred Tax Assets, Net of Valuation Allowance							82,262,000	97,980,000
Deferred Tax Liabilities, Net							430,593,000	391,063,000
Internal Revenue Service (IRS)
Tax Audits [Abstract]
Year(s) under examination		2012 and 2013.				2010 and 2011
Year of carryback claim under examination						2009
Tax Adjustments, Settlements, and Unusual Provisions			$ 14,000,000
Operating Loss Carryforwards							97,000,000	103,000,000
Tax Credit Carryforward, Amount							4,000,000	5,000,000
Carryforward expiration date range, low			2021
Carryforward expiration date range, high			2036
WISCONSIN
Tax Audits [Abstract]
Year(s) under examination	2012 and 2013
State and Local Jurisdiction
Tax Audits [Abstract]
Operating Loss Carryforwards							$ 3,000,000	$ 3,000,000
Carryforward expiration date range, high			2031
Consolidated Appropriations Act of 2016; 2015, 2016, 2017 Impact [Member]
Consolidated Appropriations Act of 2016 [Abstract]
Bonus depreciation rate, Percent							50.00%
Consolidated Appropriations Act of 2016; 2018 Impact [Member]
Consolidated Appropriations Act of 2016 [Abstract]
Bonus depreciation rate, Percent							40.00%
Production Tax Credit Rate, Percent							60.00%
Consolidated Appropriations Act of 2016; 2019 Impact [Member]
Consolidated Appropriations Act of 2016 [Abstract]
Bonus depreciation rate, Percent							30.00%
Production Tax Credit Rate, Percent							40.00%
Investment Tax Credit Rate, Percent							30.00%
Consolidated Appropriations Act of 2016; 2016 Impact [Member]
Consolidated Appropriations Act of 2016 [Abstract]
Production Tax Credit Rate, Percent							100.00%
Production Tax Credit per KWh | $ / kWh							0.023
Consolidated Appropriations Act of 2016; 2017 Impact [Member]
Consolidated Appropriations Act of 2016 [Abstract]
Production Tax Credit Rate, Percent							80.00%
Consolidated Appropriations Act of 2016; 2020 Impact [Member]
Consolidated Appropriations Act of 2016 [Abstract]
Investment Tax Credit Rate, Percent							26.00%
Consolidated Appropriations Act of 2016; 2021 Impact [Member]
Consolidated Appropriations Act of 2016 [Abstract]
Investment Tax Credit Rate, Percent							22.00%
Consolidated Appropriations Act of 2016; After 2021 Impact [Member]
Consolidated Appropriations Act of 2016 [Abstract]
Investment Tax Credit Rate, Percent							10.00%
Tax Increase Prevention Act of 2014; 2014 Impact [Member]
Consolidated Appropriations Act of 2016 [Abstract]
Bonus depreciation rate, Percent								50.00%
Tax Increase Prevention Act of 2014; 2015 Impact [Member]
Consolidated Appropriations Act of 2016 [Abstract]
Bonus depreciation rate, Percent							50.00%