Share Repurchase Activity (Parenthetical) (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Stockholders Equity Note [Line Items]
Average purchase price for shares	$ 40.67	$ 38.56	$ 39.12	$ 37.49