Balance Sheets Parenthetical - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Nuclear fuel; fuel in process	$ 69,533	$ 59,689
Allowance for Doubtful Accounts Receivable, Current	$ 1,820	$ 2,300
Common Stock, Par or Stated Value Per Share	$ 1	$ 1
Common Stock, Shares Authorized	100,000,000	100,000,000
Common Stock, Shares Issued	65,666,420	65,694,829
Common stock, Restricted shares	162,268	133,859
Treasury Stock, Shares	25,166,943	25,244,350