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Additional Information with Respect to Options Granted, Vested and Exercised (Detail) - USD ($) $ / shares in Units, $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |  |  |
Weighted-average grant date fair value of stock options granted (per share) |  |  | $ 4.90
Aggregate grant date fair value of stock options vested during the year | $ 1,954 | $ 4,565 | $ 4,729
Aggregate intrinsic value of stock options exercised |  | $ 209 | $ 366

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- Definition Share-based Compensation Arrangement by Share-based Payment Award, Grant Date Fair Value of Options Vested. + References No definition available. + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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