Loans and Allowance for Losses - Schedule of Concentrations of Risk by Risk Factor (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 7,776,950	$ 7,233,971
Less than $1,000,000
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	2,455,109	2,431,296
$1,000,000 to $4,999,999
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	2,812,060	2,755,996
$5,000,000 to $9,999,999
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	1,003,021	916,422
$10,000,000 to $24,999,999
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	773,658	601,349
$25,000,000 and greater
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	733,102	528,908
0.00% to 40.00%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 1,418,075	1,333,790
Loan-to-value ratio range, lower range limit	0.00%
Loan-to-value ratio range, upper range limit	40.00%
40.01% to 50.00%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 2,008,307	1,811,166
Loan-to-value ratio range, lower range limit	40.01%
Loan-to-value ratio range, upper range limit	50.00%
50.01% to 60.00%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 2,616,272	2,530,484
Loan-to-value ratio range, lower range limit	50.01%
Loan-to-value ratio range, upper range limit	60.00%
60.01% to 70.00%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 1,385,116	1,244,823
Loan-to-value ratio range, lower range limit	60.01%
Loan-to-value ratio range, upper range limit	70.00%
70.01% to 80.00%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 329,979	289,427
Loan-to-value ratio range, lower range limit	70.01%
Loan-to-value ratio range, upper range limit	80.00%
80.01% to 90.00%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 19,201	24,281
Loan-to-value ratio range, lower range limit	80.01%
Loan-to-value ratio range, upper range limit	90.00%
Crops
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 3,930,858	3,771,627
Permanent Plantings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	1,727,261	1,509,821
Livestock
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	1,502,887	1,355,372
Part-time Farm
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	532,065	504,138
Ag. Storage and Processing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	76,466	85,181
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	7,413	7,832
Northwest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	982,222	855,596
Southwest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	2,573,691	2,273,184
Mid-North
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	2,358,592	2,296,073
Mid-South
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	947,544	883,279
Northeast
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	321,794	332,370
Southeast
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 593,107	$ 593,469