Balance Sheets Parenthetical - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Nuclear fuel; fuel in process	$ 57,845	$ 61,709
Accounts Receivable, Allowance for Credit Loss, Current	$ 1,778	$ 1,900
Common Stock, Par or Stated Value Per Share	$ 1	$ 1
Common Stock, Shares Authorized	100,000,000	100,000,000
Common Stock, Shares, Issued	64,312,516	64,332,884
Common stock, Restricted shares	116,172	95,804
Treasury Stock, Shares	23,656,061	23,696,262