Loans and Allowance for Losses and Concentrations of Credit Risk - Allowance for Credit Losses Roll Forward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Allowance for Loan Losses	$ 5,415
Beginning Balance - Reserve for Losses	2,020
Beginning Balance - Total Allowance for Losses	7,435	$ 6,563
Provision for loan losses	(637)	(49)
(Release of)/provision for reserve for losses	(193)	14
Financing Receivable, Allowance for Credit Losses, Write-downs	(241)	0
Total provision for losses	444	63
Ending Balance - Allowance for Loan Losses	5,811
Ending Balance - Reserve for Losses	1,827
Ending Balance - Total Allowance for Losses	7,638	6,626
Crops [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	3,365	2,791
Financing Receivable, Allowance for Credit Losses, Write-downs	(228)
Total provision for losses	425	101
Ending Balance - Total Allowance for Losses	3,562	2,892
Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	1,723	931
Financing Receivable, Allowance for Credit Losses, Write-downs	0
Total provision for losses	147	6
Ending Balance - Total Allowance for Losses	1,870	937
Livestock [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	1,375	1,781
Financing Receivable, Allowance for Credit Losses, Write-downs	(13)
Total provision for losses	17	(18)
Ending Balance - Total Allowance for Losses	1,379	1,763
Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	405	408
Financing Receivable, Allowance for Credit Losses, Write-downs	0
Total provision for losses	(81)	36
Ending Balance - Total Allowance for Losses	324	444
Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	533	649
Financing Receivable, Allowance for Credit Losses, Write-downs	0
Total provision for losses	(61)	(62)
Ending Balance - Total Allowance for Losses	472	587
Other Commodity [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	34	3
Financing Receivable, Allowance for Credit Losses, Write-downs	0
Total provision for losses	(3)	0
Ending Balance - Total Allowance for Losses	31	3
Allowance for Loan and Lease Losses [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Allowance for Loan Losses	5,415	4,480
Provision for loan losses	(637)	(49)
Financing Receivable, Allowance for Credit Losses, Write-downs	(241)	0
Ending Balance - Allowance for Loan Losses	5,811	4,529
Reserve for Off-balance Sheet Activities [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Reserve for Losses	2,020	2,083
(Release of)/provision for reserve for losses	(193)	14
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Ending Balance - Reserve for Losses	$ 1,827	$ 2,097