Equity - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 20, 2012	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Stockholders Equity Note [Line Items]
Dividend, payment date	Jun. 20, 2012
Dividends declared and paid per share	$ 0.45	$ 0.45	$ 0.45	$ 0.90	$ 0.90
Dividend record date	Jun. 06, 2012
Dividend equivalents on restricted stock units expected to vest				$ 2.9	$ 2.6
Common Stock
Stockholders Equity Note [Line Items]
Repurchased common stock				350,206	372,262
Average repurchase price of common stock				$ 35.69	$ 51.63
Restricted Stock Units
Stockholders Equity Note [Line Items]
Restricted stock units vested and issued as common stock				419,908	585,368
Repurchased shares for award				152,187	256,778
Average repurchase price of shares for award		$ 46.55	$ 69.32	$ 46.55	$ 69.32