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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 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		7,084	$ 10,576	6,563	$ 10,127
(Provision for)/release of loan losses		(191)	1,164	(604)	978
(Release of)/provision for reserve for losses		(222)	861	(114)	1,235
Financing Receivable, Allowance for Credit Losses, Write-downs		(130)	0	(130)	(111)
Total (release of)/provision for losses		(31)	(303)	490	257
Ending Balance - Allowance for Loan Losses		4,954		4,954
Ending Balance - Reserve for Losses		1,969		1,969
Ending Balance - Total Allowance for Losses		6,923	10,273	6,923	10,273
Crops [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses		3,111	2,653	2,791	2,519
Financing Receivable, Allowance for Credit Losses, Write-downs		0	0	0	0
Total (release of)/provision for losses		103	110	423	244
Ending Balance - Total Allowance for Losses		3,214	2,763	3,214	2,763
Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses		1,144	2,221	931	2,159
Financing Receivable, Allowance for Credit Losses, Write-downs		0	0	0	0
Total (release of)/provision for losses		198	(1,151)	411	(1,089)
Ending Balance - Total Allowance for Losses		1,342	1,070	1,342	1,070
Livestock [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses		1,906	1,760	1,781	1,423
Financing Receivable, Allowance for Credit Losses, Write-downs		0	0	0	0
Total (release of)/provision for losses		(354)	39	(229)	376
Ending Balance - Total Allowance for Losses		1,552	1,799	1,552	1,799
Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses		447	433	408	467
Financing Receivable, Allowance for Credit Losses, Write-downs		(130)	0	(130)	(111)
Total (release of)/provision for losses		36	(49)	75	28
Ending Balance - Total Allowance for Losses		353	384	353	384
Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses		473	3,502	649	3,552
Financing Receivable, Allowance for Credit Losses, Write-downs		0	0	0	0
Total (release of)/provision for losses		(13)	748	(189)	698
Ending Balance - Total Allowance for Losses		460	4,250	460	4,250
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	0	0
Total (release of)/provision for losses		(1)	0	(1)	0
Ending Balance - Total Allowance for Losses		2	7	2	7
Allowance for Loan and Lease Losses [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Allowance for Loan Losses		4,893	5,939	4,480	5,864
(Provision for)/release of loan losses		(191)	1,164	(604)	978
Financing Receivable, Allowance for Credit Losses, Write-downs		(130)	0	(130)	(111)
Ending Balance - Allowance for Loan Losses		4,954	4,775	4,954	4,775
Reserve for Off-balance Sheet Activities [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Reserve for Losses		2,191	4,637	2,083	4,263
(Release of)/provision for reserve for losses		(222)	861	(114)	1,235
Financing Receivable, Allowance for Credit Losses, Write-downs		0	0	0	0
Ending Balance - Reserve for Losses		$ 1,969	$ 5,498	$ 1,969	$ 5,498

[1] Includes loans and loans underlying off-balance sheet Farm & Ranch Guaranteed Securities (excluding AgVantage 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.