Computations 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
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Numerator for basic and diluted EPS - net income allocated to common stockholders	$ 2,242	$ 21,483	$ 18,376	$ 19,902
Denominator for basic EPS - weighted average number of shares	30,507,700	31,009,869	30,649,957	31,178,508
Add - dilutive effect of:
Weighted average number of incremental shares issuable from restricted stock units	5,000	1,000	6,000	9,000
Denominator for diluted EPS - weighted average number of shares and dilutive potential shares	30,512,613	31,010,524	30,656,429	31,187,576
Earnings per share:
Basic	$ 0.07	$ 0.69	$ 0.60	$ 0.64
Diluted	$ 0.07	$ 0.69	$ 0.60	$ 0.64