Notes Receivable - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013 Receivables	Sep. 30, 2012	Sep. 30, 2013 Receivables	Sep. 30, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of notes receivable	2		2
Interest income	$ 3,020,000	$ 3,081,000	$ 9,123,000	$ 9,256,000
Payment received relating to notes receivables			13,300,000	15,500,000
National Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 3,000,000	$ 3,100,000	$ 9,100,000	$ 9,200,000