U.S. Statutory Federal Income Tax Rate and Tax (Benefit) Expense (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Rate Reconciliation [Line Items]
Statutory U.S. federal income tax rate	35.00%	35.00%	35.00%