Changes in the Corporation's liability of estimated losses from credit recourses agreements (Detail) (Financial Guarantee Member, USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Financial Guarantee Member
Guarantor Obligations [Line Items]
Balance as of beginning of period	$ 47,983	$ 56,115	$ 51,673	$ 58,659
Valuation Allowances And Reserves Charged To Other Accounts	0	0	0	0
Provision	6,688	5,330	10,785	9,562
Valuation Allowances And Reserves Deductions	(8,779)	(5,662)	(16,566)	(12,438)
Balance as of end of period	$ 45,892	$ 55,783	$ 45,892	$ 55,783