Fair Value Disclosures of Financial Assets (Assets Measured At Fair Value On Recurring Basis) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended	3 Months Ended	9 Months Ended			3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2012	Jun. 30, 2012	Sep. 30, 2012	Dec. 31, 2011	Mar. 31, 2012 Trading Securities [Member]	Sep. 30, 2012 Trading Securities [Member]	Jun. 30, 2012 Trading Securities [Member]	Dec. 31, 2010 Trading Securities [Member]	Mar. 31, 2012 Reverse Mortgages [Member]	Jun. 30, 2012 Reverse Mortgages [Member]	Sep. 30, 2012 Reverse Mortgages [Member]	Dec. 31, 2011 Reverse Mortgages [Member]	Mar. 31, 2012 Available-For-Sale Securities [Member]	Jun. 30, 2012 Available-For-Sale Securities [Member]	Sep. 30, 2012 Available-For-Sale Securities [Member]	Dec. 31, 2011 Available-For-Sale Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Balance	$ 15,722	$ 15,722	$ 15,722	$ 11,746	$ 12,432	$ 12,432	$ 12,465	$ 12,432	$ (646)	$ (646)	$ (646)	$ (686)	$ 3,936	$ 3,936	$ 3,936
Total net (losses) income for the period included in net income	4	(47)	35	128	33				(29)	(47)	35	(137)				265
Purchases, sales, issuances, and settlements, net	45	45	45	2,932					45	45	45	177				2,755
Mark-to-market adjustment	(436)	845	1,830	916		125							(436)	845	1,705	916
Balance	$ 15,335	$ 16,178	$ 18,088	$ 15,722	$ 12,465	$ 12,590	$ 12,465	$ 12,432	$ (630)	$ (632)	$ (552)	$ (646)	$ 3,500	$ 4,345	$ 6,050	$ 3,936