Changes in Stock Appreciation Rights (Parenthetical) (Detail) (SARs)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
SARs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued upon exercise of SARs	9,818	20,229	372,499