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
Numerator:
Income (loss)	$ 6,455	$ 13,432	$ 4,754	$ 24,497
Denominator:
Denominator for basic earnings per share - Weighted-average shares	16,309,053	15,944,483	16,270,955	15,918,978
Effect of dilutive stock options	555,000	733,000	572,000	685,000
Denominator for diluted earnings per share - Adjusted weighted-average shares and assumed conversions	16,864,166	16,678,377	16,842,768	16,603,543
Basic income (loss) per share:	$ 0.40	$ 0.84	$ 0.29	$ 1.54
Diluted income (loss) per share:	$ 0.38	$ 0.81	$ 0.28	$ 1.48