Balance Sheet Offsetting - Financial Instruments Eligible for Offset Consolidated Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Financial assets	$ 2,424	$ 2,246	$ 6,818
Gross Amount Offset, Financial assets
Net Amount Recognized, Financial assets	2,424	2,246	6,818
Gross Amount Recognized, Resell agreements, Financial assets	4,898	4,898	8,052
Gross Amount Offset, Resell agreements, Financial assets
Net Amount Recognized, Resell agreements, Financial assets	4,898	4,898	8,052
Gross Amount Recognized, Financial assets	7,322	7,144	14,870
Gross Amount Offset, Financial assets
Net Amount Recognized, Financial assets	7,322	7,144	14,870
Gross Amount Recognized, Financial liabilities	68,942	74,159	83,587
Gross Amount Offset, Financial liabilities
Net Amount Recognized, Financial liabilities	68,942	74,159	83,587
Gross Amount Recognized, Repurchase agreements, Financial liabilities	508,702	559,461	635,248
Gross Amount Offset, Repurchase agreements, Financial liabilities
Net Amount Recognized, Repurchase agreements, Financial liabilities	508,702	559,461	635,248
Gross Amount Recognized, Financial liabilities	577,644	633,620	718,835
Gross Amount Offset, Financial liabilities
Net Amount Recognized, Financial liabilities	577,644	633,620	718,835
Loan/lease interest rate swaps and caps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Financial assets	262	36	28
Gross Amount Offset, Financial assets
Net Amount Recognized, Financial assets	262	36	28
Commodity Swaps and Options [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Financial assets	2,159	2,207	6,790
Gross Amount Offset, Financial assets
Net Amount Recognized, Financial assets	2,159	2,207	6,790
Gross Amount Recognized, Financial liabilities	4,430	1,614	11,326
Gross Amount Offset, Financial liabilities
Net Amount Recognized, Financial liabilities	4,430	1,614	11,326
Foreign currency forward contracts [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Financial assets	3	3
Gross Amount Offset, Financial assets
Net Amount Recognized, Financial assets	3	3
Gross Amount Recognized, Financial liabilities	207		6
Gross Amount Offset, Financial liabilities
Net Amount Recognized, Financial liabilities	207		6
Loan Lease Interest Rate Swaps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Financial liabilities	60,999	68,180	65,050
Gross Amount Offset, Financial liabilities
Net Amount Recognized, Financial liabilities	60,999	68,180	65,050
Interest Rate Swap On Junior Subordinated Deferrable Interest Debentures [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Financial liabilities	3,306	4,365	7,205
Gross Amount Offset, Financial liabilities
Net Amount Recognized, Financial liabilities	$ 3,306	$ 4,365	$ 7,205