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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 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	$ 7,638	$ 6,626	7,435	$ 6,563
Provision for loan losses	(327)	(364)	(964)	(413)
Provision for/(release of) reserve for losses	139	94	(54)	108
Financing Receivable, Allowance for Credit Losses, Write-downs		0	(241)	0
Total provision for losses	466	458	910	521
Ending Balance - Allowance for Loan Losses	6,138		6,138
Ending Balance - Reserve for Losses	1,966		1,966
Ending Balance - Total Allowance for Losses	8,104	7,084	8,104	7,084
Crops [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	3,562	2,892	3,365	2,791
Financing Receivable, Allowance for Credit Losses, Write-downs			(228)
Total provision for losses	173	219	598	320
Ending Balance - Total Allowance for Losses	3,735	3,111	3,735	3,111
Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	1,870	937	1,723	931
Financing Receivable, Allowance for Credit Losses, Write-downs			0
Total provision for losses	294	207	441	213
Ending Balance - Total Allowance for Losses	2,164	1,144	2,164	1,144
Livestock [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	1,379	1,763	1,375	1,781
Financing Receivable, Allowance for Credit Losses, Write-downs			(13)
Total provision for losses	(145)	143	(128)	125
Ending Balance - Total Allowance for Losses	1,234	1,906	1,234	1,906
Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	324	444	405	408
Financing Receivable, Allowance for Credit Losses, Write-downs			0
Total provision for losses	73	3	(8)	39
Ending Balance - Total Allowance for Losses	397	447	397	447
Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	472	587	533	649
Financing Receivable, Allowance for Credit Losses, Write-downs			0
Total provision for losses	86	(114)	25	(176)
Ending Balance - Total Allowance for Losses	558	473	558	473
Other Commodity [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses	31	3	34	3
Financing Receivable, Allowance for Credit Losses, Write-downs			0
Total provision for losses	(15)	0	(18)	0
Ending Balance - Total Allowance for Losses	16	3	16	3
Allowance for Loan and Lease Losses [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Allowance for Loan Losses	5,811	4,529	5,415	4,480
Provision for loan losses	(327)	(364)	(964)	(413)
Financing Receivable, Allowance for Credit Losses, Write-downs	0		(241)	0
Ending Balance - Allowance for Loan Losses	6,138	4,893	6,138	4,893
Reserve for Off-balance Sheet Activities [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Reserve for Losses	1,827	2,097	2,020	2,083
Provision for/(release of) reserve for losses	139	94	(54)	108
Financing Receivable, Allowance for Credit Losses, Write-downs			0	0
Ending Balance - Reserve for Losses	$ 1,966	$ 2,191	$ 1,966	$ 2,191