Loans and Allowance for Losses and Concentrations of Credit Risk - Allowance for Credit Losses Roll Forward (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 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	$ 9,431	$ 13,979	10,127	$ 13,334
(Provision for)/release of allowance for loan losses	(110)	1,583	(186)	1,010
Provision for/(release of) reserve for losses	1,146	(974)	374	(873)
Total (release of)/provision for losses	1,256	(2,557)	560	(1,883)
Financing Receivable, Allowance for Credit Losses, Write-downs	(111)	(57)	(111)	(86)
Ending Balance - Allowance for Loan Losses	5,939		5,939
Ending Balance - Reserve for Losses	4,637		4,637
Ending Balance - Total Allowance for Losses	10,576	11,365	10,576	11,365
Crops [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	2,640	2,278	2,519	2,124
Total (release of)/provision for losses	13	112	134	266
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	0	0
Ending Balance - Total Allowance for Losses	2,653	2,390	2,653	2,390
Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	2,284	2,131	2,159	2,186
Total (release of)/provision for losses	(63)	86	62	31
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	0	0
Ending Balance - Total Allowance for Losses	2,221	2,217	2,221	2,217
Livestock [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	1,343	1,387	1,423	1,271
Total (release of)/provision for losses	417	(19)	337	97
Financing Receivable, Allowance for Credit Losses, Write-downs	0	(57)	0	(57)
Ending Balance - Total Allowance for Losses	1,760	1,311	1,760	1,311
Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	459	464	467	454
Total (release of)/provision for losses	85	(20)	77	19
Financing Receivable, Allowance for Credit Losses, Write-downs	(111)	0	(111)	(29)
Ending Balance - Total Allowance for Losses	433	444	433	444
Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	2,698	7,715	3,552	7,292
Total (release of)/provision for losses	804	(2,716)	(50)	(2,293)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	0	0
Ending Balance - Total Allowance for Losses	3,502	4,999	3,502	4,999
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
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	5,940	7,410	5,864	6,866
(Provision for)/release of allowance for loan losses	(110)	1,583	(186)	1,010
Financing Receivable, Allowance for Credit Losses, Write-downs	(111)	(57)	(111)	(86)
Ending Balance - Allowance for Loan Losses	5,939	5,770	5,939	5,770
Reserve for Off-balance Sheet Activities [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Reserve for Losses	3,491	6,569	4,263	6,468
Provision for/(release of) reserve for losses	1,146	(974)	374	(873)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	0	0
Ending Balance - Reserve for Losses	$ 4,637	$ 5,595	$ 4,637	$ 5,595