Summary of Stock Option Activity (Detail) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Shares Under Option
Outstanding at beginning of period	3,995
Granted	1,221	200	540
Exercised	(197)
Cancelled/forfeited/expired	(293)
Outstanding at end of period	4,726	3,995
Vested and expected to vest at end of period	4,677
Exercisable at end of period	713
Weighted Average Exercise Price
Outstanding at beginning of period	$ 20.75
Granted	$ 13.22
Exercised	$ 7.09
Cancelled/forfeited/expired	$ 28.43
Outstanding at end of period	$ 18.90	$ 20.75
Vested and expected to vest at end of period	$ 18.96
Exercisable at end of period	$ 7.09
Weighted Average Remaining Contractual Term (years)
Outstanding at end of period	5 years 10 months 24 days	6 years 2 months 12 days
Granted	9 years 2 months 12 days
Vested and expected to vest at end of period	6 years 2 months 12 days
Exercisable at end of period	6 years 2 months 12 days
Aggregate Intrinsic Value
Outstanding at beginning of period	$ 9.5
Outstanding at end of period	2.1	9.5
Vested and expected to vest at end of period	2.1
Exercisable at end of period	$ 1.4