Notes Receivable - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Average estimated default rate for the Company's pool of receivables	9.70%
Result of change in projected default rate	0.10%
Default rate change impact on loan loss reserve	$ 4
Maximum outstanding period for note receivable being delinquent	30 days
Number of days loan consider to be in default	120 days