Impaired Loans and Valuation Allowance for Loan Losses - Loan Portfolio and Related Allowance (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Carrying Value	$ 54,233	$ 88,629
Individually Evaluated for Impairment, Associated Allowance	5,177	8,518
Collectively Evaluated for Impairment, Carrying Value	1,208,679	1,113,849
Collectively Evaluated for Impairment, Associated Allowance	15,239	14,601
Carrying Value, Total	1,262,912	1,202,478
Associated Allowance, Total	20,416	23,119
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Carrying Value	3,855	4,525
Individually Evaluated for Impairment, Associated Allowance	173	444
Collectively Evaluated for Impairment, Carrying Value	58,911	51,688
Collectively Evaluated for Impairment, Associated Allowance	674	835
Carrying Value, Total	62,766	56,213
Associated Allowance, Total	847	1,279
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Carrying Value	13,723	44,833
Individually Evaluated for Impairment, Associated Allowance	684	3,533
Collectively Evaluated for Impairment, Carrying Value	485,347	428,970
Collectively Evaluated for Impairment, Associated Allowance	6,157	6,880
Carrying Value, Total	499,070	473,803
Associated Allowance, Total	6,841	10,413
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Carrying Value	35,953	38,281
Individually Evaluated for Impairment, Associated Allowance	4,202	4,440
Collectively Evaluated for Impairment, Carrying Value	546,623	524,140
Collectively Evaluated for Impairment, Associated Allowance	7,107	6,061
Carrying Value, Total	582,576	562,421
Associated Allowance, Total	11,309	10,501
Commercial and Financial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Carrying Value	24	37
Individually Evaluated for Impairment, Associated Allowance	0	1
Collectively Evaluated for Impairment, Carrying Value	70,755	58,185
Collectively Evaluated for Impairment, Associated Allowance	659	334
Carrying Value, Total	70,779	58,222
Associated Allowance, Total	659	335
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Carrying Value	678	953
Individually Evaluated for Impairment, Associated Allowance	118	100
Collectively Evaluated for Impairment, Carrying Value	47,043	50,866
Collectively Evaluated for Impairment, Associated Allowance	642	491
Carrying Value, Total	47,721	51,819
Associated Allowance, Total	$ 760	$ 591