Treasury Stock - Additional Information (Detail) (USD $)	0 Months Ended		9 Months Ended		12 Months Ended
	Feb. 08, 2013	Nov. 19, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Equity, Class of Treasury Stock [Line Items]
Common stock repurchase, remaining authorized amount					$ 350,100,000
Common stock purchased through modified dutch auction tender offer - in shares	5,524,861
Common stock purchased through modified dutch auction tender offer - price per share	$ 45.25
Common Stock Purchased Through Modified Dutch Auction Tender Offer Value	250,000,000
Dollar amount of common stock intended to purchase through modified dutch auction tender offer		250,000,000
Common stock purchased through modified dutch auction tender offer - Fees and expenses incurred	1,000,000
Repurchase of common stock			267,607,000	33,863,000
Treasury shares issued			149,304
Issuance of treasury shares, average cost per share			$ 6.63
Shares repurchased to satisfy employee withholding tax requirements resulting from certain restricted stock units becoming vested			58,812
Common stock repurchased, average cost (in dollars per share)			$ 43.55
Treasury stock, shares			24,140,804
Common Stock Repurchase Progam (excluding Dutch Auction purchases)
Equity, Class of Treasury Stock [Line Items]
Common stock repurchase, remaining authorized amount			83,500,000
Repurchases of common stock (in shares)			354,154
Average cost per share of stock acquired (in dollars per share)			$ 46.90
Repurchase of common stock			$ 16,600,000