Stock Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended					3 Months Ended	12 Months Ended			12 Months Ended		1 Months Ended	12 Months Ended				1 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 Stock options	Dec. 31, 2012 Stock and stock units	Dec. 31, 2011 Stock and stock units	Dec. 31, 2010 Stock and stock units	Mar. 31, 2012 Performance share units	Dec. 31, 2012 Performance share units	Mar. 31, 2011 Performance share units	Mar. 31, 2012 Performance share units Maximum	Dec. 31, 2012 Restricted shares or units	Dec. 31, 2012 Stock Option Plan, 2006	Jun. 30, 2008 Employee Stock Purchase Plan	Dec. 31, 2012 Employee Stock Purchase Plan	Dec. 31, 2011 Employee Stock Purchase Plan	Dec. 31, 2010 Employee Stock Purchase Plan	Dec. 31, 1997 Employee Stock Purchase Plan	Jun. 30, 2008 Employee Stock Purchase Plan Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting period		4 years
Stock options, expiration period		10 years
Shares available for awards under the plan											12,790,684
Reserved common stock for issuance under the plan																500,000
Additional shares of common stock reserved												500,000
Purchase price of common stock by employees																	85.00%
Payroll withholding period for purchase of shares of common stock												3 months
Shares of common stock issued under the plan													66,531	87,331	176,318
Stock options remaining contractual term	10 years
Total unrecognized compensation cost related to non vested stock options outstanding	$ 35.6
Weighted average period of compensation cost expected to be recognized		3 years 2 months 12 days								1 year 9 months 18 days
Total fair value of stock and stock unit awards vested			27.8	8.0	1.6
Unrecognized compensation expense									$ 8.5	$ 7.5
Number of performance share units			1,903,445	2,785,026		352,000		392,500
Performance share units vesting percentage							50.00%
Performance share units vesting percentage after one year							50.00%
Performance share units vesting date						Dec. 31, 2016