Treasury Stock - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended		3 Months Ended	12 Months Ended
	Feb. 08, 2013	Nov. 19, 2012	Mar. 31, 2013	Dec. 31, 2012
Equity, Class of Treasury Stock [Line Items]
Common stock repurchase, remaining authorized amount			$ 100.1	$ 350.1
Dollar amount of common stock intended to purchase through modified dutch auction tender offer		250.0
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 - total purchase price in dollars	250.0
Common stock purchased through modified dutch auction tender offer - Fees and expenses incurred	$ 1.0
Treasury shares issued			119,880
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			50,559
Common stock repurchased, average cost			$ 42.74
Treasury stock, shares			23,807,821