Open Market Share Repurchase Program - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended
	Sep. 09, 2012	Sep. 09, 2011	Sep. 09, 2012	Sep. 11, 2011	Sep. 30, 2012 Repurchase of Equity
Share Repurchases [Line Items]
Common stock repurchased and retired (in shares)	189,718	3,163,060	1,336,215	5,268,550	106,573
Common stock repurchased and retired	$ 5,900,000	$ 81,900,000	$ 42,719,000	$ 129,190,000	$ 3,700,000
Stock repurchase program, amount remaining	197,900,000
Stock repurchase program, approved amount	$ 200,000,000		$ 200,000,000
Shares of common stock outstanding	56,846,578		56,846,578