Guarantees and Long-Term Standby Purchase Commitments - Cash Flows from Off-balance sheet Guaranteed Securities (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Guarantor Obligations [Line Items]
Proceeds from new securitizations	$ 116,708	$ 131,202
Guarantee fees received	442	546
Purchases of assets from the trusts(1)	$ (4,721)	$ (721)
Farmer Mac Guaranteed Securities [Member]
Guarantor Obligations [Line Items]
Weighted average remaining maturity, loans underlying guarantees not held by transferor	10 years 3 months 15 days		10 years 3 months 15 days
Farmer Mac Guaranteed Securities [Member] | Unconsolidated VIEs [Member]
Guarantor Obligations [Line Items]
Guarantor obligation, liability	$ 2,700		$ 2,800
Institutional Credit [Member] | Farmer Mac Guaranteed Securities [Member]
Guarantor Obligations [Line Items]
Weighted average remaining maturity, loans underlying guarantees not held by transferor	4 years 7 months 90 days		5 years 15 days