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Summary of Option Activity (Detail) - Incentive Stock Options
3 Months Ended
Mar. 31, 2019
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Incentive Stock Option Plans, Beginning balance | shares 384,064
Incentive Stock Option Plans, Option exercised | shares (14,677)
Incentive Stock Option Plans, Ending balance | shares 369,387
Weighted Average Price Per Share, Beginning balance | $ / shares $ 9.10
Weighted Average Price Per Share, Option exercised | $ / shares 9.18
Weighted Average Price Per Share, Ending balance | $ / shares $ 9.10