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Income Per Common Share - Additional Information (Detail) - shares | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Earnings Per Share [Abstract] |  |  |
Dilutive effect of outstanding restricted stock awards after application of the Treasury Stock Method | 117,000 | 61,000 | 36,000

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- Definition Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 28A -URI http://asc.fasb.org/extlink&oid=96947427&loc=d3e1500-109256 + Details
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