Earnings per Share - Common Stock Equivalents Not Included in Computation of Diluted Earnings Per Share (Detail) - $ / shares	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	55,607	26,022
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	61,065	24,375
Minimum [Member] | Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Net Income, Per Outstanding Unit, Amount	$ 13.96	$ 9.26
Minimum [Member] | Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Net Income, Per Outstanding Unit, Amount	14.17	15.09
Maximum [Member] | Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Net Income, Per Outstanding Unit, Amount	14.49	13.96
Maximum [Member] | Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Net Income, Per Outstanding Unit, Amount	$ 15.83	$ 15.09