Summary of Stock Option Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Options
Outstanding at January 1, 2012	2,849,000
Granted			347,000
Exercised	(1,268,000)
Forfeited	(68,000)
Outstanding at December 31, 2012	1,513,000	2,849,000
Expected to Vest at December 31, 2012	1,307,000
Exercisable at December 31, 2012	893,000
Weighted Average Exercise Price
Outstanding at January 1, 2012	$ 13.78
Granted
Exercised	$ 12.43
Forfeited	$ 16.21
Outstanding at December 31, 2012	$ 14.81	$ 13.78
Expected to Vest at December 31, 2012	$ 14.79
Exercisable at December 31, 2012	$ 13.62
Weighted Average Remaining Contractual Term
Outstanding at December 31, 2012	4 years 10 months 28 days
Expected to Vest at December 31, 2012	4 years 8 months 27 days
Exercisable at December 31, 2012	3 years 10 months 24 days
Aggregate Intrinsic Value
Outstanding at January 1, 2012	$ 41,252,000
Granted
Exercised	(20,033,000)	(5,500,000)	(848,000)
Forfeited	(783,000)
Outstanding at December 31, 2012	20,373,000	41,252,000
Expected to Vest at December 31, 2012	17,632,000
Exercisable at December 31, 2012	$ 13,093,000
Weighted Average Fair Value
Outstanding at January 1, 2012	$ 6.38
Granted			$ 10.31
Exercised	$ 5.91
Forfeited	$ 7.38
Outstanding at December 31, 2012	$ 6.74	$ 6.38
Expected to Vest at December 31, 2012	$ 6.80
Exercisable at December 31, 2012	$ 5.93