Loans and Allowance for Losses and Concentrations of Credit Risk - Allowance for Credit Losses Roll Forward (Details) - USD ($)		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities, Subject To Be Purchased	[1]	$ 100,000				$ 0				$ 100,000	$ 0
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Allowance for Loan Losses					$ 4,480,000					4,480,000
Beginning Balance - Reserve for Losses					2,083,000					2,083,000
Beginning Balance - Total Allowance for Losses					6,563,000				$ 10,127,000	6,563,000	10,127,000	$ 13,334,000
(Provision for)/release of loan losses		(461,000)	$ (191,000)	$ (364,000)	(49,000)	(3,366,000)	$ 1,164,000	$ (110,000)	(76,000)	(1,065,000)	(2,388,000)	961,000
Release of reserve for losses										(63,000)	(2,180,000)	(2,205,000)
Financing Receivable, Allowance for Credit Losses, Write-downs										(130,000)	(3,772,000)	(86,000)
Financing Receivable, Allowance for Credit Losses, Recovery												45,000
Total (release of)/provision for losses										1,002,000	208,000	(3,166,000)
Ending Balance - Allowance for Loan Losses		5,415,000				4,480,000				5,415,000	4,480,000
Ending Balance - Reserve for Losses		2,020,000				2,083,000				2,020,000	2,083,000
Ending Balance - Total Allowance for Losses		7,435,000				6,563,000				7,435,000	6,563,000	10,127,000
Crops [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses					2,791,000				2,519,000	2,791,000	2,519,000
Financing Receivable, Allowance for Credit Losses, Write-downs										0	0
Total (release of)/provision for losses										574,000	272,000
Ending Balance - Total Allowance for Losses		3,365,000				2,791,000				3,365,000	2,791,000	2,519,000
Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses					931,000				2,159,000	931,000	2,159,000
Financing Receivable, Allowance for Credit Losses, Write-downs										0	0
Total (release of)/provision for losses										792,000	(1,228,000)
Ending Balance - Total Allowance for Losses		1,723,000				931,000				1,723,000	931,000	2,159,000
Livestock [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses					1,781,000				1,423,000	1,781,000	1,423,000
Financing Receivable, Allowance for Credit Losses, Write-downs										0	0
Total (release of)/provision for losses										(406,000)	358,000
Ending Balance - Total Allowance for Losses		1,375,000				1,781,000				1,375,000	1,781,000	1,423,000
Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses					408,000				467,000	408,000	467,000
Financing Receivable, Allowance for Credit Losses, Write-downs										(130,000)	(111,000)
Total (release of)/provision for losses										127,000	52,000
Ending Balance - Total Allowance for Losses		405,000				408,000				405,000	408,000	467,000
Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses					649,000				3,552,000	649,000	3,552,000
Financing Receivable, Allowance for Credit Losses, Write-downs										0	(3,661,000)
Total (release of)/provision for losses										(116,000)	758,000
Ending Balance - Total Allowance for Losses		533,000				649,000				533,000	649,000	3,552,000
Other Commodity [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Total Allowance for Losses					3,000				7,000	3,000	7,000
Financing Receivable, Allowance for Credit Losses, Write-downs										0	0
Total (release of)/provision for losses										31,000	(4,000)
Ending Balance - Total Allowance for Losses		34,000				3,000				34,000	3,000	7,000
Allowance for Loan and Lease Losses [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Allowance for Loan Losses					4,480,000				5,864,000	4,480,000	5,864,000	6,866,000
(Provision for)/release of loan losses										(1,065,000)	(2,388,000)	961,000
Financing Receivable, Allowance for Credit Losses, Write-downs												(86,000)
Ending Balance - Allowance for Loan Losses		5,415,000				4,480,000				5,415,000	4,480,000	5,864,000
Reserve for Off-balance Sheet Activities [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance - Reserve for Losses					$ 2,083,000				$ 4,263,000	2,083,000	4,263,000	6,468,000
Release of reserve for losses										(63,000)	(2,180,000)	(2,205,000)
Financing Receivable, Allowance for Credit Losses, Write-downs										0	0	0
Financing Receivable, Allowance for Credit Losses, Recovery												0
Ending Balance - Reserve for Losses		$ 2,020,000				$ 2,083,000				$ 2,020,000	$ 2,083,000	$ 4,263,000

[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 with at least one missed payment, excluding loans performing under either their original loan terms or a court-approved bankruptcy plan.