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Stock - Based Compensation - Summary of Accumulated Stock Units (Detail) - $ / shares | Dec. 31, 2017 | Dec. 31, 2016
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Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |  |
Accumulated stock units | 138,768 | 140,044
Average price | $ 22.84 | $ 20.87

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- Definition Deferred compensation arrangement with individual accumulated stock units For deferred board fees. + References No definition available. + Details
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- Definition Deferred compensation arrangement with individual stock average price. + References No definition available. + Details
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- References No definition available. + Details
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