Loans and Allowance for Losses - Schedule of Concentrations of Risk by Risk Factor (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 7,215,585	$ 7,233,971
Less than $1,000,000 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	2,446,989	2,431,296
$1,000,000 to $4,999,999 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	2,736,397	2,755,996
$5,000,000 to $9,999,999 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	881,847	916,422
$10,000,000 to $24,999,999 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	604,712	601,349
$25,000,000 and greater [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	545,640	528,908
Financing Receivables, Original Loan-To-Value Ratio, Range One [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 1,304,411	1,333,790
Loan-to-value ratio range, lower range limit	0.00%
Loan-to-value ratio range, upper range limit	40.00%
Financing Receivables, Original Loan-To-Value Ratio, Range Two [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 1,831,552	1,811,166
Loan-to-value ratio range, lower range limit	40.01%
Loan-to-value ratio range, upper range limit	50.00%
Financing Receivables, Original Loan-To-Value Ratio, Range Three [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 2,506,962	2,530,484
Loan-to-value ratio range, lower range limit	50.01%
Loan-to-value ratio range, upper range limit	60.00%
Financing Receivables, Original Loan-To-Value Ratio, Range Four [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 1,250,982	1,244,823
Loan-to-value ratio range, lower range limit	60.01%
Loan-to-value ratio range, upper range limit	70.00%
Financing Receivables, Original Loan-To-Value Ratio, Range Five [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 298,001	289,427
Loan-to-value ratio range, lower range limit	70.01%
Loan-to-value ratio range, upper range limit	80.00%
Financing Receivables, Original Loan-To-Value Ratio, Range Six [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 23,677	24,281
Loan-to-value ratio range, lower range limit	80.01%
Loan-to-value ratio range, upper range limit	90.00%
Northwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 847,896	855,596
Southwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	2,282,664	2,273,184
Mid-North [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	2,287,199	2,296,073
Mid-South [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	893,639	883,279
Northeast [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	337,019	332,370
Southeast [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	567,168	593,469
Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	3,763,456	3,771,627
Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	1,492,359	1,509,821
Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	1,350,610	1,355,372
Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	517,110	504,138
Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	84,321	85,181
Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross financing receivables	$ 7,729	$ 7,832