Fully Vested and Exercisable Stock Options and Stock Options Expected to Vest (Detail) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2011 Year
Fully Vested and Exercisable
Total shares	2,105
Weighted-average exercise price	$ 6.67
Aggregate intrinsic value	$ 2,828,900
Weighted-average remaining contractual term, in years	6.4
Expected to Vest
Total shares	4,245
Weighted-average exercise price	$ 6.13
Aggregate intrinsic value	$ 4,701,402
Weighted-average remaining contractual term, in years	7.5