Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Net income	$ 9,604	$ 4,284	$ 20,466	$ 18,594
Weighted average shares outstanding - basic	27,829,555	30,321,909	28,223,321	30,311,658
Net income per share	$ 0.35	$ 0.14	$ 0.73	$ 0.61
Weighted average shares outstanding - diluted	27,836,453	30,367,556	28,236,562	30,349,985
Net income per share	$ 0.35	$ 0.14	$ 0.72	$ 0.61