Activity for Stock Options (Detail) (Stock Options, USD $) In Millions, except Share data in Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Year
Stock Options
Number of Option Shares
Outstanding at beginning of period	2,381
Granted	425
Exercised	(464)
Cancelled/expired/forfeited	(79)
Outstanding at end of period	2,263	[1]
Exercisable at end of period	1,191
Weighted-Average Remaining Contractual Term
Outstanding at end of period	4.5	[1]
Exercisable at end of period	3.7
Aggregate Intrinsic Value
Outstanding at end of period	$ 0.9	[1]
Exercisable at end of period	$ 6.0
Weighted-Average Exercise Price
Outstanding at beginning of period	$ 7.42
Granted	$ 25.35
Exercised	$ 5.29
Cancelled/expired/forfeited	$ 15.04
Outstanding at end of period	$ 10.96	[1]
Exercisable at end of period	$ 6.36

[1] Of the remaining shares subject to outstanding options, we expect approximately 1.1 million shares to vest at a weighted-average exercise price of $16.07.