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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator:
Net income	$ 10,361	$ 5,093	$ 30,766	$ 25,857
Less: Income allocated to participating securities	(94)	(47)	(297)	(271)
Net income available to common stockholders	$ 10,267	$ 5,046	$ 30,469	$ 25,586
Denominator:
Weighted average shares - basic	65,288	64,961	65,197	64,854
Performance-based restricted stock awards		8		7
Weighted average shares - diluted	65,288	64,969	65,197	64,861
Basic net income per share:
Net income	$ 0.16	$ 0.08	$ 0.47	$ 0.39
Diluted net income per share:
Net income	$ 0.16	$ 0.08	$ 0.47	$ 0.39