Summarized Quarterly Financial Data (Unaudited) - Summary of Unaudited Quarterly Financial Results of Operations (Parenthetical) (Detail) (USD $)	3 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
One-time loss recorded on early extinguishment of debt	$ 10,200,000	$ 10,180,000
One-time loss recorded on early extinguishment of debt, after tax	6,600,000	6,600,000
Redemption of senior unsecured notes	$ 250,000,000