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Share-based Compensation - Summary of Transactions for Non-Vested Stock Options (Detail) - $ / shares | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward] |  |  |
Number of Shares, Non-vested options outstanding at beginning of period | 46,340 | 176,688 | 379,106
Number of Shares, Options granted | 0 | 0 | 28,000
Number of Shares, Options vested | (37,005) | (130,223) | (158,810)
Number of Shares, Options forfeited | 0 | (125) | (71,608)
Number of Shares, Non-vested options outstanding at end of period | 9,335 | 46,340 | 176,688
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] |  |  |
Weighted-Average Exercise Price Per Share, Non-vested options outstanding at beginning of period (in usd per share) | $ 22.42 | $ 19.13 | $ 18.11
Weighted-Average Exercise Price Per Share, Options granted (in usd per share) | 0.00 | 0.00 | 23.47
Weighted-Average Exercise Price Per Share, Options vested (in usd per share) | 22.16 | 17.83 | 16.80
Weighted-Average Exercise Price Per Share, Options forfeited (in usd per share) | 0.00 | 144.00 | 20.59
Weighted-Average Exercise Price Per Share, Non-vested options outstanding at end of period (in usd per share) | $ 23.47 | $ 22.42 | $ 19.13

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- Definition Gross number of share options (or share units) granted during the period. + References No definition available. + 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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Number of non-vested options outstanding. + References No definition available. + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Number of non-vested options forfeited. + References No definition available. + Details
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- Definition Weighted average grant-date fair value of non-vested options forfeited. + References No definition available. + Details
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- Definition Weighted average grant-date fair value of non-vested options outstanding. + References No definition available. + Details
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- References No definition available. + Details
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- Definition Number of options vested. + References No definition available. + Details
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- Definition Weighted average grant-date fair value of options vested. + References No definition available. + Details
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