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Statements of Common Stockholders' Equity (Unaudited) (Parenthetical) - $ / shares
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Cash dividends declared (in dollars per share) $ 0.1874 $ 0.1802 $ 0.3748 $ 0.3604