Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Allowance for uncollectible accounts	$ 0	$ 0
Shareholders’ equity:
Common stock, shares authorized	240,000,000	240,000,000
Common stock, shares issued	148,888,000	148,203,000