Revolving Line of Credit - Maximum Consolidated Leverage Ratio (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2012
Maximum [Member]
Line of Credit Facility [Line Items]
Consolidated Leverage Ratio	2.00%	1.50%
Minimum [Member]
Line of Credit Facility [Line Items]
Consolidated Leverage Ratio	1.00%	1.00%