Computation of Basic and Diluted Earnings per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator:
Net income	$ 5,093	$ 5,995	$ 25,857	$ 17,716
Less: Income allocated to participating securities	(47)	(62)	(271)	(214)
Net income available to common stockholders	$ 5,046	$ 5,933	$ 25,586	$ 17,502
Denominator:
Weighted average shares - basic	64,961	64,586	64,854	64,458
Performance-based restricted stock awards	8	18	7	17
Weighted average shares - diluted	64,969	64,604	64,861	64,475
Basic net income per share:
Net income	$ 0.08	$ 0.09	$ 0.39	$ 0.27
Diluted net income per share:
Net income	$ 0.08	$ 0.09	$ 0.39	$ 0.27