Balance Sheets Parenthetical - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Nuclear fuel; fuel in process	$ 71,715	$ 57,315
Allowance for Doubtful Accounts Receivable, Current	$ 2,432	$ 2,156
Common Stock, Par or Stated Value Per Share	$ 1	$ 1
Common Stock, Shares Authorized	100,000,000	100,000,000
Common Stock, Shares, Issued	65,666,808	65,685,615
Common stock, restricted shares	161,880	137,017
Treasury Stock, Shares	25,236,894	25,304,914