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Shareholders' Equity - Reconciliation of Weighted Average Number of Shares (Detail) - shares
shares in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Weighted Average Number of Shares Outstanding [Line Items]      
Weighted average number of common shares outstanding 61,109 62,236 62,668
Director Plan and deferred stock units 207 177 157
ESOP 121 100 91
Common shares outstanding—basic 61,437 62,513 62,916
Common and potential common shares outstanding—diluted 62,292 63,949 64,180
Restricted Stock      
Weighted Average Number of Shares Outstanding [Line Items]      
Dilutive effect of stock awards 581 679 384
Stock Options      
Weighted Average Number of Shares Outstanding [Line Items]      
Dilutive effect of stock awards 274 757 880