Summary of Transactions Relating to Common Stock (Parenthetical) (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stockholders Equity Note [Line Items]
Repurchase of common stock	5,890,238	3,918,719	306,032
Repurchase of common stock, value	$ 211,986	$ 99,820	$ 3,744
ValueAct Capital Master Fund Limited Partnership
Stockholders Equity Note [Line Items]
Repurchase of common stock	2,148,434
Repurchase of common stock, value	$ 75,200