Summary of Stock Option Activity (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Shares Under Option
Outstanding at beginning of period	4,726,000
Cancelled/forfeited/expired	(345,000)
Outstanding at end of period	4,381,000	4,726,000
Vested and expected to vest at March 31, 2013	4,332,000
Exercisable at end of period	1,093,000
Weighted Average Exercise Price
Outstanding at beginning of period	$ 18.90
Cancelled/forfeited/expired	$ 18.42
Outstanding at end of period	$ 18.93	$ 18.90
Vested and expected to vest at March 31, 2013	$ 19.00
Exercisable at end of period	$ 7.09
Weighted Average Remaining Contractual Term (years)
Outstanding	6 years 4 months 24 days	6 years 2 months 12 days
Vested and expected to vest at March 31, 2013	6 years 4 months 24 days
Exercisable at March 31, 2013	5 years 10 months 24 days
Aggregate Intrinsic Value
Outstanding at beginning of period	$ 2.1
Outstanding at end of period	5.4	2.1
Vested and expected to vest at March 31, 2013	5.4
Exercisable at end of period	$ 5.4