STATEMENTS OF CAPITALIZATION - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Long-Term Debt
Unamortized discount (premium), net	$ 605	$ (309)
Total long-term debt, including current maturities	1,550,605	1,349,691
Less: current maturities	200,000	0
Long-term debt	1,350,605	1,349,691
Common Stockholder's Equity
Common stock — 200 shares authorized of $1.00 par value; 100 shares outstanding at Dec. 31, 2015 and 2014, respectively	0	0
Additional paid in capital	1,371,223	1,165,463
Retained earnings	438,007	395,998
Accumulated other comprehensive loss	(1,281)	(989)
Total common stockholder’s equity	1,807,949	1,560,472
First Mortgage Bonds | Series Due June 15, 2024
Long-Term Debt
Principal outstanding	350,000	150,000
First Mortgage Bonds | Series Due Aug. 15, 2041
Long-Term Debt
Principal outstanding	400,000	400,000
Unsecured Senior Notes | Senior E Due Oct. 1, 2016
Long-Term Debt
Principal outstanding	200,000	200,000
Unsecured Senior Notes | Senior G Due Dec. 1, 2018
Long-Term Debt
Principal outstanding	250,000	250,000
Unsecured Senior Notes | Senior C and D Due Oct. 1, 2033
Long-Term Debt
Principal outstanding	100,000	100,000
Unsecured Senior Notes | Senior F Due Oct. 1, 2036
Long-Term Debt
Principal outstanding	$ 250,000	$ 250,000