Fair Value Disclosures - Summary of Carrying Value and Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financial assets:
Financial derivatives	$ 13,470	$ 16,123
Guarantee and commitment fees receivable	39,038	37,113
Financial liabilities:
Financial derivatives	149,556	182,371
Guarantee and commitment obligation	37,526	35,535
Fair Value
Financial assets:
Cash and cash equivalents	899,052	1,033,941
Loans	9,526,315	9,167,525
Financial derivatives	15,668	17,468
Guarantee and commitment fees receivable	36,643	34,115
Financial liabilities:
Notes payable	22,448,508	22,130,263
Debt securities of consolidated trusts held by third parties	1,039,150	1,390,330
Financial derivatives	25,633	29,892
Guarantee and commitment obligation	35,131	32,537
Fair Value | Investment securities:
Financial assets:
Marketable securities	3,742,635	3,899,925
Fair Value | Farmer Mac Guaranteed Securities
Financial assets:
Marketable securities	8,393,490	8,148,691
Fair Value | USDA Securities:
Financial assets:
Marketable securities	2,548,207	2,637,509
Carrying Amount
Financial assets:
Cash and cash equivalents	899,052	1,033,941
Loans	9,022,915	8,535,146
Financial derivatives	15,668	17,468
Guarantee and commitment fees receivable	39,038	37,113
Financial liabilities:
Notes payable	22,365,121	21,848,917
Debt securities of consolidated trusts held by third parties	990,961	1,323,786
Financial derivatives	25,633	29,892
Guarantee and commitment obligation	37,526	35,535
Carrying Amount | Investment securities:
Financial assets:
Marketable securities	3,741,639	3,898,724
Carrying Amount | Farmer Mac Guaranteed Securities
Financial assets:
Marketable securities	8,387,062	8,123,493
Carrying Amount | USDA Securities:
Financial assets:
Marketable securities	$ 2,462,010	$ 2,480,321