FDIC Indemnification Asset (Detail) - Schedule of changes in FDIC indemnification asset (USD $) In Thousands, unless otherwise specified	3 Months Ended				3 Months Ended	12 Months Ended			3 Months Ended	12 Months Ended			3 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012	Sep. 30, 2011	Dec. 31, 2011 Gross Receivable [Member]	Dec. 31, 2012 Gross Receivable [Member]	Sep. 30, 2011 Gross Receivable [Member]	Sep. 30, 2010 Gross Receivable [Member]	Dec. 31, 2011 Discount [Member]	Dec. 31, 2012 Discount [Member]	Sep. 30, 2011 Discount [Member]	Sep. 30, 2010 Discount [Member]	Dec. 31, 2011 Net Receivable [Member]	Dec. 31, 2012 Net Receivable [Member]	Sep. 30, 2011 Net Receivable [Member]	Sep. 30, 2010 Net Receivable [Member]
Balance	$ 51,021		$ 80,268	$ 50,465	$ 51,213	$ 80,801	$ 50,946	$ 70,079	$ (192)	$ (533)	$ (481)	$ (2,496)	$ 51,021	$ 80,268	$ 50,465	$ 67,583
Establish indemnification asset related to Plantation						36,641				(721)				35,920
Payments from FDIC for losses on covered assets					(14)	(13,467)	(19,212)		0				(14)	(13,467)	(19,212)
Amortization of potential impairment	830	1,180				(3,986)								(3,986)
Valuation adjustment on covered assets					281	10,400	79		0				281	10,400	79
Discount accretion					$ 0				$ 289	$ 380	$ 2,015		$ 289	$ 380	$ 2,015