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Summary of Performance option activity (Detail) - Performance Based Stock Options
3 Months Ended
Mar. 31, 2021
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Incentive Stock Option Plans, Beginning balance | shares 114,658
Incentive Stock Option Plans, Ending balance | shares 114,658
Weighted Average Price Per Share, Beginning balance | $ / shares $ 11.49
Weighted Average Price Per Share, Ending balance | $ / shares $ 11.49