Computation of Basic and Diluted Earnings Per Share (Parenthetical) (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
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	253,500	4,981,879	253,500	4,981,879
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	$ 22.14	$ 15.40	$ 22.14	$ 15.40