Loans and Allowance for Losses and Concentrations of Credit Risk - Allowance for Credit Losses Roll Forward (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Allowance for Loan Losses			$ 5,864
Beginning Balance - Reserve for Losses			4,263
Beginning Balance - Total Allowance for Losses	$ 10,576	$ 11,365	10,127	$ 13,334
Release of/(provision for) allowance for loan losses	1,164	(511)	978	499
Provision for/(release of) reserve for losses	861	(1,315)	1,235	(2,188)
Total (release of)/provision for losses	(303)	(804)	257	(2,687)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	(111)	(86)
Financing Receivable, Allowance for Credit Losses, Recovery	0	45	0	45
Ending Balance - Allowance for Loan Losses	4,775		4,775
Ending Balance - Reserve for Losses	5,498		5,498
Ending Balance - Total Allowance for Losses	10,273	10,606	10,273	10,606
Crops [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	2,653	2,390	2,519	2,124
Total (release of)/provision for losses	110	123	244	389
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	0	0
Financing Receivable, Allowance for Credit Losses, Recovery		0		0
Ending Balance - Total Allowance for Losses	2,763	2,513	2,763	2,513
Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	2,221	2,217	2,159	2,186
Total (release of)/provision for losses	(1,151)	74	(1,089)	105
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	0	0
Financing Receivable, Allowance for Credit Losses, Recovery		45		45
Ending Balance - Total Allowance for Losses	1,070	2,336	1,070	2,336
Livestock [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	1,760	1,311	1,423	1,271
Total (release of)/provision for losses	39	(6)	376	91
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	0	(57)
Financing Receivable, Allowance for Credit Losses, Recovery		0		0
Ending Balance - Total Allowance for Losses	1,799	1,305	1,799	1,305
Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	433	444	467	454
Total (release of)/provision for losses	(49)	(3)	28	16
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	(111)	(29)
Financing Receivable, Allowance for Credit Losses, Recovery		0		0
Ending Balance - Total Allowance for Losses	384	441	384	441
Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	3,502	4,999	3,552	7,292
Total (release of)/provision for losses	748	(992)	698	(3,285)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	0	0
Financing Receivable, Allowance for Credit Losses, Recovery		0		0
Ending Balance - Total Allowance for Losses	4,250	4,007	4,250	4,007
Other Commodity [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	7	4	7	7
Total (release of)/provision for losses	0	0	0	(3)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	0	0
Financing Receivable, Allowance for Credit Losses, Recovery		0		0
Ending Balance - Total Allowance for Losses	7	4	7	4
Allowance for Loan and Lease Losses [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Allowance for Loan Losses	5,939	5,770	5,864	6,866
Release of/(provision for) allowance for loan losses	1,164	(511)	978	499
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	(111)	(86)
Financing Receivable, Allowance for Credit Losses, Recovery	0	45		45
Ending Balance - Allowance for Loan Losses	4,775	6,326	4,775	6,326
Reserve for Off-balance Sheet Activities [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Reserve for Losses	4,637	5,595	4,263	6,468
Provision for/(release of) reserve for losses	861	(1,315)	1,235	(2,188)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	0	0
Financing Receivable, Allowance for Credit Losses, Recovery	0	0		0
Ending Balance - Reserve for Losses	$ 5,498	$ 4,280	$ 5,498	$ 4,280