Loans and Allowance for Credit Losses - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loan portfolio as commercial loan	82.00%		82.00%
Risk rated loans	$ 1,000		$ 1,000
Percentage of credit exposure to risk based capital	25.00%		25.00%
Loans and other extensions of credit granted to directors, executive officers, and their related entities	$ 9,700		$ 9,700		$ 10,600
Amount drawn from loans and other extensions of credit granted	7,100		7,100		6,800
Commercial loans held-for-sale	12,290		12,290		17,585
Mortgage loans held-for-sale	62,600		62,600		61,600
Loans sold			1,300,000	$ 788,100
Gain (Loss) on Sale of Mortgage Loans	19,500	$ 7,400	47,655	$ 18,291
Loans and Leases Receivable, Net of Deferred Income	22,477,409		22,477,409		$ 19,787,876
Paycheck Protection Program [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 2,300,000		$ 2,300,000
Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of credit exposure to risk based capital	86.70%		86.70%		83.60%
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	268.80%		268.80%		268.30%