Computation of Basic and Diluted Earnings Per Share (Parenthetical) (Detail) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Earnings Per Share Basic And Diluted By Common Class [Line Items]
Denominator for basic earnings per common share—weighted-average shares	47,512		47,707
Basic weighted-average common shares outstanding and non-vested restricted stock expected to vest	47,750		47,962
Percentage allocated to common shareholders	99.50%	[1]	99.50%	[1]

[1] (1) Basic weighted-average common shares outstanding47,51247,707 Basic weighted-average common shares outstanding and non-vested restricted stock expected to vest47,75047,962 Percentage allocated to common shareholders99.5%99.5%