Loans and Allowance for Loan Losses - Narrative (Details) loan in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) loan	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) loan	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable Including Other Real Estated Owned [Line Items]
Commercial, industrial, commercial real estate or construction loans, held for investment, period of time after payment becomes delinquent that the Company stops accruing interest income and applies subsequent interest payments as principal reductions			90 days
Consumer loans including residential real estate, held for investment, period of time after payment becomes delinquent or when foreclosure proceedings have been initiated that the Company stops accruing interest income			90 days
Number of loan deferrals | loan	63		63
Loan deferrals, amortized cost	$ 7,200,000		$ 7,200,000
Loan deferrals, deferred principal	129,700		129,700
Loan deferrals, interest balances	77,100		77,100
Impact to the allowance for loan losses related to modifications classified as TDRs	(108)	$ 7,900	5,200	$ 11,600
Commitments to lend additional funds to borrowers whose terms have been modified in a TDR	41,300		41,300		$ 43,800
Other real estate owned	15,000		15,000		22,000
Loans secured by residential real estate properties for which formal foreclosure proceedings were in process	40,000		40,000		57,000
Other assets
Accounts, Notes, Loans and Financing Receivable Including Other Real Estated Owned [Line Items]
Accrued interest receivable	229,000		229,000		205,000
Interest Rate Concession
Accounts, Notes, Loans and Financing Receivable Including Other Real Estated Owned [Line Items]
TDRs	4,300	4,800	9,500	9,500
Modification of Loan Structure
Accounts, Notes, Loans and Financing Receivable Including Other Real Estated Owned [Line Items]
TDRs	25,500	$ 17,000	69,100	$ 32,800
Residential real estate – mortgage
Accounts, Notes, Loans and Financing Receivable Including Other Real Estated Owned [Line Items]
Other real estate owned	$ 8,000		$ 8,000		$ 14,000
Maximum
Accounts, Notes, Loans and Financing Receivable Including Other Real Estated Owned [Line Items]
Recognition of charge off expenses on consumer loans, period of time loan is past due			120 days
Recognition of charge off expenses on residential loans, period of time loan is past due			180 days
Recognition of charge off expenses on credit card loans, period of time loan is past due			180 days