Notes Receivable - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014 Note	Sep. 30, 2013	Sep. 30, 2014 Note	Sep. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of notes receivable	2		2
Interest income	$ 3,001,000	$ 3,020,000	$ 9,070,000	$ 9,123,000
National Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of notes receivable	2		2
Interest income	3,000,000	3,000,000	9,100,000	9,100,000
Payment received relating to notes receivables			$ 10,800,000	$ 13,300,000