Loans and Allowance for Credit Losses - Troubled Debt Restructurings, Excluding Loans Acquired, Segregated by Class of Loans (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($) loan	Mar. 31, 2020 loan	Dec. 31, 2020 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	0	0
Extended Maturity and Payment Deferral | COVID-19 Pandemic
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	3,700		3,700
Troubled debt, balance | $	$ 3,000,000		$ 3,000,000
Extended Maturity and Payment Deferral | COVID-19 Pandemic | Assisted living
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	1
Troubled debt, balance | $	$ 17,310
Extended Maturity and Payment Deferral | COVID-19 Pandemic | Transportation
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	5
Troubled debt, balance | $	$ 783
Extended Maturity and Payment Deferral | COVID-19 Pandemic | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	37
Troubled debt, balance | $	$ 3,776
Extended Maturity and Payment Deferral | COVID-19 Pandemic | Hotel
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	17
Troubled debt, balance | $	$ 152,864
Extended Maturity and Payment Deferral | COVID-19 Pandemic | Food service
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	3
Troubled debt, balance | $	$ 2,683
Extended Maturity and Payment Deferral | COVID-19 Pandemic | All other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	16
Troubled debt, balance | $	$ 31,029
Extended Maturity and Payment Deferral | COVID-19 Pandemic | Total
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	79
Troubled debt, balance | $	$ 208,445
Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	54		54
Troubled debt, balance | $	$ 7,283		$ 7,513
Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	35		32
Troubled debt, balance | $	$ 3,805		$ 3,138
Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	19		22
Troubled debt, balance | $	$ 3,478		$ 4,375
Real Estate | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	48		48
Troubled debt, balance | $	$ 5,180		$ 5,260
Real Estate | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	32		29
Troubled debt, balance | $	$ 3,181		$ 2,512
Real Estate | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	16		19
Troubled debt, balance | $	$ 1,999		$ 2,748
Real Estate | Single family residential | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	46		46
Troubled debt, balance | $	$ 5,124		$ 5,199
Real Estate | Single family residential | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	31		28
Troubled debt, balance | $	$ 3,133		$ 2,463
Real Estate | Single family residential | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	15		18
Troubled debt, balance | $	$ 1,991		$ 2,736
Real Estate | Other commercial | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	2		2
Troubled debt, balance | $	$ 56		$ 61
Real Estate | Other commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	1		1
Troubled debt, balance | $	$ 48		$ 49
Real Estate | Other commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	1		1
Troubled debt, balance | $	$ 8		$ 12
Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	6		6
Troubled debt, balance | $	$ 2,103		$ 2,253
Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	3		3
Troubled debt, balance | $	$ 624		$ 626
Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	3		3
Troubled debt, balance | $	$ 1,479		$ 1,627
Commercial | Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	6		6
Troubled debt, balance | $	$ 2,103		$ 2,253
Commercial | Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	3		3
Troubled debt, balance | $	$ 624		$ 626
Commercial | Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	3		3
Troubled debt, balance | $	$ 1,479		$ 1,627