XML 21 R59.htm IDEA: XBRL DOCUMENT v3.20.1
Reconciliation of Earnings and Share Data used in Basic and Diluted Earnings per Share Computations (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Earnings Per Share [Abstract]    
Net earnings available to Alleghany stockholders $ (361,218) $ 440,227
Effect of dilutive securities (3,000)  
Income available to common stockholders for diluted earnings per share $ (364,200) $ 440,200
Weighted average common shares outstanding applicable to basic earnings per share 14,340,669 14,481,255
Effect of dilutive securities 15,439 3,981
Adjusted weighted average common shares outstanding applicable to diluted earnings per share 14,356,108 14,485,236
Contingently issuable shares [1] 18,703 39,325
[1] Contingently issuable shares were potentially available in the periods presented, but were not included in the diluted earnings per share computations because the impact was anti-dilutive to the earnings per share calculation.