Member Loans and Notes and Certificates Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 1,516,676	$ 781,215
Fair Value	1,522,975	785,316
Fair Value, Measurements, Recurring | Notes And Certificates At Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate principal balance outstanding	1,540,631	795,842
Fair valuation adjustments	(17,656)	(10,526)
Fair Value	1,522,975	785,316
Fair Value, Measurements, Recurring | Member Loans At Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate principal balance outstanding	1,534,340	791,774
Fair valuation adjustments	(17,664)	(10,559)
Fair Value	$ 1,516,676	$ 781,215