Changes in Level 3 Instrument Measured on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 7,372	$ 7,494
Instruments attributable to discontinued operations		(168)
Total realized and unrealized gains	75	1,821
Purchases, issuances, and settlements		172
Principal repayments	(1,417)	(1,947)
Balance at end of period	$ 6,030	$ 7,372