CONSOLIDATED STATEMENTS OF CAPITALIZATION - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Schedule of Capitalization, Long-term Debt [Line Items]
Unamortized discount		$ (2,869)	$ (2,865)
Unamortized Debt Issuance Expense		(6,505)	(4,697)
Total long-term debt, including current maturities		761,180	663,069
Less: current maturities		151,080	1,123
Total long-term debt		610,100	661,946
Common Stockholders' Equity
Common stock — 1,000,000 shares authorized of $100 par value; 933,000 shares outstanding at Dec. 31, 2017 and 2016, respectively		93,300	93,300
Additional paid in capital		449,350	395,315
Retained earnings		334,008	323,368
Accumulated other comprehensive loss		(69)	(133)
Total common stockholder’s equity		876,589	811,850
First Mortgage Bonds | Series Due Oct. 1, 2018
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross		150,000	150,000
First Mortgage Bonds | Series Due June 15, 2024
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross		200,000	200,000
First Mortgage Bonds | Series Due Sept. 1, 2038
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross		200,000	200,000
First Mortgage Bonds | Series Due Oct. 1, 2042
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross		100,000	100,000
First Mortgage Bonds | Series Due Dec. 1, 2047
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross		100,000	0
City of La Crosse Resource Recovery Bond | Series Due Nov. 1, 2021
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross	[1]	18,600	18,600
Other
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term debt, gross		$ 1,954	$ 2,031

[1] Resource recovery financing