Loans and Allowance for Credit Losses - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loan portfolio as commercial loan	78.20%
Risk rated loans	$ 1,000
Percentage of credit exposure to risk based capital	25.00%
Loans and other extensions of credit granted to directors, executive officers, and their related entities	$ 8,200		$ 10,700
Amount drawn from loans and other extensions of credit granted	5,600		6,800
Commercial loans held-for-sale	12,541		31,200
Mortgage loans held-for-sale	71,700		67,800
Loans sold	547,000	$ 286,700
Gain (Loss) on Sale of Mortgage Loans	13,666	$ 8,583
Loans and Leases Receivable, Net of Deferred Income	23,086,701		22,424,501
Section 4013 Cares Act Loan Modifications	835,100
Paycheck Protection Program [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 2,200,000		$ 1,800,000
Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of credit exposure to risk based capital	76.00%		89.00%
Non-owner occupied commercial real estate and multifamily loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of credit exposure to risk based capital	256.00%		264.00%