Summary of Stock Options Outstanding (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Options Outstanding
Number of options	8,228,334	7,381,329
Weighted average exercise price per share	$ 10.20	$ 5.22
Aggregate intrinsic value (in 000's)	$ 78,839
Weighted average remaining contractual term (years)	6 years 11 months 5 days
Options Exercisable
Number of options	4,086,791
Weighted average exercise price per share	$ 5.67
Aggregate intrinsic value (in 000's)	55,296
Weighted average remaining contractual term (years)	4 years 10 months 10 days
Options vested and expected to vest
Number of options	8,039,905
Weighted average exercise price per share	$ 10.23
Aggregate intrinsic value (in 000's)	$ 76,870
Weighted average remaining contractual term (years)	6 years 10 months 24 days

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