Computation of Basic and Diluted Earnings per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator:
Net income	$ 11,303	$ 11,030	$ 20,244	$ 20,405
Less: Income allocated to participating securities	(104)	(109)	(190)	(203)
Net income available to common stockholders	$ 11,199	$ 10,921	$ 20,054	$ 20,202
Denominator:
Weighted average shares - basic	65,588	65,245	65,488	65,151
Performance-based restricted stock awards	0	0	0	0
Weighted average shares - diluted	65,588	65,245	65,488	65,151
Basic net income per share:
Net income	$ 0.17	$ 0.17	$ 0.31	$ 0.31
Diluted net income per share:
Net income	$ 0.17	$ 0.17	$ 0.31	$ 0.31