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, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities, Subject To Be Purchased	[1]	$ 300		$ 300		$ 0
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Allowance for Loan Losses				4,480
Beginning Balance - Reserve for Losses				2,083
Beginning Balance - Total Allowance for Losses		6,626	$ 9,431	6,563	$ 10,127
Provision for loan losses		(364)	(110)	(413)	(186)
Provision for reserve for losses		94	1,146	108	374
Financing Receivable, Allowance for Credit Losses, Write-downs		0	(111)	0	(111)
Total (release of)/provision for losses		458	1,256	521	560
Ending Balance - Allowance for Loan Losses		4,893		4,893
Ending Balance - Reserve for Losses		2,191		2,191
Ending Balance - Total Allowance for Losses		7,084	10,576	7,084	10,576
Crops [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses		2,892	2,640	2,791	2,519
Financing Receivable, Allowance for Credit Losses, Write-downs			0		0
Total (release of)/provision for losses		219	13	320	134
Ending Balance - Total Allowance for Losses		3,111	2,653	3,111	2,653
Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses		937	2,284	931	2,159
Financing Receivable, Allowance for Credit Losses, Write-downs			0		0
Total (release of)/provision for losses		207	(63)	213	62
Ending Balance - Total Allowance for Losses		1,144	2,221	1,144	2,221
Livestock [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses		1,763	1,343	1,781	1,423
Financing Receivable, Allowance for Credit Losses, Write-downs			0		0
Total (release of)/provision for losses		143	417	125	337
Ending Balance - Total Allowance for Losses		1,906	1,760	1,906	1,760
Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses		444	459	408	467
Financing Receivable, Allowance for Credit Losses, Write-downs			(111)		(111)
Total (release of)/provision for losses		3	85	39	77
Ending Balance - Total Allowance for Losses		447	433	447	433
Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses		587	2,698	649	3,552
Financing Receivable, Allowance for Credit Losses, Write-downs			0		0
Total (release of)/provision for losses		(114)	804	(176)	(50)
Ending Balance - Total Allowance for Losses		473	3,502	473	3,502
Other Commodity [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses		3	7	3	7
Financing Receivable, Allowance for Credit Losses, Write-downs			0		0
Total (release of)/provision for losses		0	0	0	0
Ending Balance - Total Allowance for Losses		3	7	3	7
Allowance for Loan and Lease Losses [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Allowance for Loan Losses		4,529	5,940	4,480	5,864
Provision for loan losses		(364)	(110)	(413)	(186)
Financing Receivable, Allowance for Credit Losses, Write-downs		0	(111)	0	(111)
Ending Balance - Allowance for Loan Losses		4,893	5,939	4,893	5,939
Reserve for Off-balance Sheet Activities [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Reserve for Losses		2,097	3,491	2,083	4,263
Provision for reserve for losses		94	1,146	108	374
Financing Receivable, Allowance for Credit Losses, Write-downs		0	0	0	0
Ending Balance - Reserve for Losses		$ 2,191	$ 4,637	$ 2,191	$ 4,637

[1] Includes loans and loans underlying off-balance sheet Farm & Ranch Guaranteed Securities and LTSPCs that are 90 days or more past due, in foreclosure, or in bankruptcy, excluding loans performing under either their original loan terms or a court-approved bankruptcy plan.