Computation of Basic and Diluted Earnings per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Numerator:
Net income	$ 9,376	$ 9,957
Less: Income allocated to participating securities	(94)	(113)
Net income available to common stockholders	$ 9,282	$ 9,844
Denominator:
Weighted average shares - basic	65,057	64,710
Performance-based restricted stock awards
Weighted average shares - diluted	65,057	64,710
Basic net income per share:
Net income	$ 0.14	$ 0.15
Diluted net income per share:
Net income	$ 0.14	$ 0.15