Computation of Basic and Diluted Earnings per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net income	$ 12,750	$ 10,361	$ 32,994	$ 30,766
Less: Income allocated to participating securities	(117)	(94)	(307)	(297)
Net income available to common stockholders	$ 12,633	$ 10,267	$ 32,687	$ 30,469
Denominator:
Weighted average shares - basic	65,618	65,288	65,532	65,197
Performance-based restricted stock awards	19		17
Weighted average shares - diluted	65,637	65,288	65,549	65,197
Basic net income per share:
Net income	$ 0.19	$ 0.16	$ 0.50	$ 0.47
Diluted net income per share:
Net income	$ 0.19	$ 0.16	$ 0.50	$ 0.47