Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Year	Dec. 31, 2010	Dec. 31, 2009
Options
Outstanding at January 1, 2011	3,374,000
Granted		347,000
Exercised	(447,000)
Forfeited	(78,000)
Outstanding at December 31, 2011	2,849,000	3,374,000
Exercisable at December 31, 2011	1,763,000
Weighted Average Exercise Price
Outstanding at January 1, 2011	$ 13.80
Granted
Exercised	$ 13.68
Forfeited	$ 15.21
Outstanding at December 31, 2011	$ 13.78	$ 13.80
Exercisable at December 31, 2011	$ 12.59
Weighted Average Remaining Contractual Term
Outstanding at December 31, 2011	4.91
Exercisable at December 31, 2011	3.52
Aggregate Intrinsic Value
Outstanding at January 1, 2011	$ 43,460
Granted
Exercised	(5,469)	(848)	(13,100)
Forfeited	(886)
Outstanding at December 31, 2011	36,760	43,460
Exercisable at December 31, 2011	$ 24,848
Weighted Average Fair Value
Outstanding at January 1, 2011	$ 6.26
Granted		$ 10.31
Exercised	$ 5.45
Forfeited	$ 6.18
Outstanding at December 31, 2011	$ 6.38	$ 6.26
Exercisable at December 31, 2011	$ 5.93