Loans and Allowance for Credit Losses - Troubled Debt Restructurings, Excluding Loans Acquired, Segregated by Class of Loans (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 loan	Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 loan	Dec. 31, 2019 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans	5	1	5	1
Extended Maturity and Payment Deferral | COVID-19 Pandemic
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			3,956
Troubled debt, balance | $	$ 3,210,944		$ 3,210,944
Extended Maturity and Payment Deferral | COVID-19 Pandemic | Real Estate Rental and Leasing
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			1,162
Troubled debt, balance | $	1,263,884		$ 1,263,884
Extended Maturity and Payment Deferral | COVID-19 Pandemic | Accommodation and Food Services
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			386
Troubled debt, balance | $	845,803		$ 845,803
Extended Maturity and Payment Deferral | COVID-19 Pandemic | Health Care and Social Assistance
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			226
Troubled debt, balance | $	278,200		$ 278,200
Extended Maturity and Payment Deferral | COVID-19 Pandemic | Construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			186
Troubled debt, balance | $	190,337		$ 190,337
Extended Maturity and Payment Deferral | COVID-19 Pandemic | Retail Trade
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			145
Troubled debt, balance | $	130,498		$ 130,498
Extended Maturity and Payment Deferral | COVID-19 Pandemic | Other Services (Except Public Administration)
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			131
Troubled debt, balance | $	58,169		$ 58,169
Extended Maturity and Payment Deferral | COVID-19 Pandemic | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			1,720
Troubled debt, balance | $	444,053		$ 444,053
Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			57		56
Troubled debt, balance | $	8,556		$ 8,556		$ 7,448
Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			35		30
Troubled debt, balance | $	3,379		$ 3,379		$ 5,887
Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			22		26
Troubled debt, balance | $	5,177		$ 5,177		$ 1,561
Real Estate | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			51		49
Troubled debt, balance | $	5,772		$ 5,772		$ 4,585
Real Estate | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			32		26
Troubled debt, balance | $	2,749		$ 2,749		$ 3,103
Real Estate | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			19		23
Troubled debt, balance | $	$ 3,023		$ 3,023		$ 1,482
Real Estate | Construction and development | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans					1
Troubled debt, balance | $					$ 72
Real Estate | Construction and development | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans					0
Troubled debt, balance | $					$ 0
Real Estate | Construction and development | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans					1
Troubled debt, balance | $					$ 72
Real Estate | Single family residential
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans	5	1	5	1
Real Estate | Single family residential | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			49		45
Troubled debt, balance | $	$ 5,708		$ 5,708		$ 3,957
Real Estate | Single family residential | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			31		25
Troubled debt, balance | $	2,700		$ 2,700		$ 2,627
Real Estate | Single family residential | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			18		20
Troubled debt, balance | $	3,008		$ 3,008		$ 1,330
Real Estate | Other commercial | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			2		3
Troubled debt, balance | $	64		$ 64		$ 556
Real Estate | Other commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			1		1
Troubled debt, balance | $	49		$ 49		$ 476
Real Estate | Other commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			1		2
Troubled debt, balance | $	15		$ 15		$ 80
Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			6		7
Troubled debt, balance | $	2,784		$ 2,784		$ 2,863
Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			3		4
Troubled debt, balance | $	630		$ 630		$ 2,784
Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			3		3
Troubled debt, balance | $	2,154		$ 2,154		$ 79
Commercial | Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			6		7
Troubled debt, balance | $	2,784		$ 2,784		$ 2,863
Commercial | Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			3		4
Troubled debt, balance | $	630		$ 630		$ 2,784
Commercial | Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans			3		3
Troubled debt, balance | $	$ 2,154		$ 2,154		$ 79