Quarterly report pursuant to Section 13 or 15(d)

Earnings per Share - Computation of Basic and Diluted Earnings Per Share, Including Antidilutive Securities Excluded from Computation of Earnings Per Share (Parenthetical) (Detail)

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Earnings per Share - Computation of Basic and Diluted Earnings Per Share, Including Antidilutive Securities Excluded from Computation of Earnings Per Share (Parenthetical) (Detail) - Restricted Stock Awards [Member] - 2013 Omnibus Equity Incentive Plan [Member]
 6 Months Ended
Jun. 30, 2018
Minimum [Member]  
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]  
Vesting period 1 year
Maximum [Member]  
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]  
Vesting period 3 years