Summary of Stock Option Activity (Detail) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Shares Under Option
Outstanding at beginning of period	4,726,000
Exercised	(88,000)
Cancelled/forfeited/expired	(361,000)
Outstanding at end of period	4,277,000	4,726,000
Vested and expected to vest at June 30, 2013	4,235,000
Exercisable at end of period	1,356,000
Weighted Average Exercise Price
Outstanding at beginning of period	$ 18.90
Exercised	$ 7.09
Cancelled/forfeited/expired	$ 18.20
Outstanding at end of period	$ 19.20	$ 18.90
Vested and expected to vest at June 30, 2013	$ 19.26
Exercisable at end of period	$ 8.68
Weighted Average Remaining Contractual Term (years)
Outstanding	6 years 2 months 12 days	6 years 2 months 12 days
Vested and expected to vest at June 30, 2013	6 years 2 months 12 days
Exercisable at June 30, 2013	6 years 6 months
Aggregate Intrinsic Value
Outstanding at beginning of period	$ 2.1
Outstanding at end of period	7.9	2.1
Vested and expected to vest at June 30, 2013	7.9
Exercisable at end of period	$ 7.2