Annual report pursuant to Section 13 and 15(d)

Earnings Per Share and Earnings Per Unit - Additional Information (Detail)

v3.8.0.1
Earnings Per Share and Earnings Per Unit - Additional Information (Detail) - shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Restricted Stock [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Securities not included in the effect of dilutive securities 133,512 107,283 152,835
Stock Options [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Securities not included in the effect of dilutive securities 13,750   5,500