Loans and Allowance for Losses - Schedule of Compositon of Loan Balances (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 4,480,511	$ 4,004,968
Allowance for loan losses	(6,753)	(7,017)
Total loans, net of allowance	6,040,088	5,515,052
Real Estate Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance	6,039,998	5,527,166
Unamortized premiums, discounts, and other cost basis adjustments	6,843	(5,097)
Total loans	6,046,841	5,522,069
Allowance for loan losses	(6,753)	(7,017)
Total loans, net of allowance	6,040,088	5,515,052
Real Estate Loan [Member] \| Farm & Ranch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance	4,610,897	4,588,323
Real Estate Loan [Member] \| Rural Utilities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance	1,429,101	938,843
Unsecuritized [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance	4,473,668	4,010,065
Unamortized premiums, discounts, and other cost basis adjustments	6,843	(5,097)
Total loans	4,480,511	4,004,968
Allowance for loan losses	(5,270)	(5,565)
Total loans, net of allowance	4,475,241	3,999,403
Unsecuritized [Member] \| Farm & Ranch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance	3,044,567	3,071,222
Unsecuritized [Member] \| Rural Utilities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance	1,429,101	938,843
In Consolidated Trusts [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance	1,566,330	1,517,101
Unamortized premiums, discounts, and other cost basis adjustments	0	0
Total loans	1,566,330	1,517,101
Allowance for loan losses	(1,483)	(1,452)
Total loans, net of allowance	1,564,847	1,515,649
In Consolidated Trusts [Member] \| Farm & Ranch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance	1,566,330	1,517,101
In Consolidated Trusts [Member] \| Rural Utilities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance	$ 0	$ 0

Unpaid principal balance of loans before unamortized premiums, discounts and other cost basis adjustments

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The reserve to cover probable credit losses related to specifically identified fixed maturity real estate loans as well as probable credit losses inherent in the remainder of that loan portfolio.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82921503&loc=d3e21338-158488

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- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

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- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6378536&loc=d3e10092-111533

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