Computation of Basic and Diluted Earnings Per Share (Parenthetical) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Options to purchase shares that were not included in the respective computation of diluted EPS because their inclusion would have had an antidilutive effect	32,400	57,400
Options to purchase shares that were not included in the respective computation of diluted EPS because their inclusion would have had an antidilutive effect, weighted average exercise prices	$ 18.15	$ 18.08