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Stock - Based Compensation - Summary of Accumulated Stock Units (Detail) - $ / shares | Mar. 31, 2018 | Dec. 31, 2017
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Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |  |
Accumulated stock units | 137,889 | 138,768
Average price | $ 23.34 | $ 22.84

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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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