Loans and Allowance for Losses and Concentrations of Credit Risk - Allowance for Credit Losses Roll Forward (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Allowance for Loan Losses	$ 5,864,000
Beginning Balance - Reserve for Losses	4,263,000
Beginning Balance - Total Allowance for Losses	10,127,000	13,334,000
Provision for loan losses	(76,000)	(573,000)
(Release of)/provision for reserve for losses	(772,000)	101,000
Total (release of)/provision for losses	(696,000)	674,000
Financing Receivable, Allowance for Credit Losses, Write-downs	0	(29,000)
Ending Balance - Allowance for Loan Losses	5,940,000
Ending Balance - Reserve for Losses	3,491,000
Ending Balance - Total Allowance for Losses	9,431,000	13,979,000
Crops [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	2,519,000	2,124,000
Total (release of)/provision for losses	121,000	154,000
Financing Receivable, Allowance for Credit Losses, Write-downs		0
Ending Balance - Total Allowance for Losses	2,640,000	2,278,000
Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	2,159,000	2,186,000
Total (release of)/provision for losses	125,000	(55,000)
Financing Receivable, Allowance for Credit Losses, Write-downs		0
Ending Balance - Total Allowance for Losses	2,284,000	2,131,000
Livestock [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	1,423,000	1,271,000
Total (release of)/provision for losses	(80,000)	116,000
Financing Receivable, Allowance for Credit Losses, Write-downs		0
Ending Balance - Total Allowance for Losses	1,343,000	1,387,000
Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	467,000	454,000
Total (release of)/provision for losses	(8,000)	39,000
Financing Receivable, Allowance for Credit Losses, Write-downs		(29,000)
Ending Balance - Total Allowance for Losses	459,000	464,000
Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	3,552,000	7,292,000
Total (release of)/provision for losses	(854,000)	423,000
Financing Receivable, Allowance for Credit Losses, Write-downs		0
Ending Balance - Total Allowance for Losses	2,698,000	7,715,000
Other Commodity [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	7,000	7,000
Total (release of)/provision for losses	0	(3,000)
Financing Receivable, Allowance for Credit Losses, Write-downs		0
Ending Balance - Total Allowance for Losses	7,000	4,000
Allowance for Loan and Lease Losses [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Allowance for Loan Losses	5,864,000	6,866,000
Provision for loan losses	(76,000)	(573,000)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	(29,000)
Ending Balance - Allowance for Loan Losses	5,940,000	7,410,000
Reserve for Off-balance Sheet Activities [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Reserve for Losses	4,263,000	6,468,000
(Release of)/provision for reserve for losses	(772,000)	101,000
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Ending Balance - Reserve for Losses	$ 3,491,000	$ 6,569,000