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Subordinated Debentures and Convertible Notes - Narrative (Details)
 3 Months Ended 12 Months Ended
Jun. 07, 2018
$ / shares
Mar. 31, 2021
USD ($)
grantorTrust
Mar. 31, 2020
USD ($)
Dec. 31, 2020
USD ($)
Jun. 06, 2018
USD ($)
Subordinated Borrowing [Line Items]          
Number of wholly owned subsidiary grantor trusts | grantorTrust   9      
Amount of pooled trust preferred securities issued   $ 126,000,000.0      
Right to defer consecutive payments of interest, maximum term   5 years      
Carrying value of Debentures   $ 104,469,000   $ 104,178,000  
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2020-06 | Additional paid-in capital          
Subordinated Borrowing [Line Items]          
Adjustments to additional paid in capital, equity component of convertible debt, net of tax   18,300,000      
Other assets          
Subordinated Borrowing [Line Items]          
Investment in common trust securities   3,900,000   3,900,000  
Carrying Value of Debentures          
Subordinated Borrowing [Line Items]          
Carrying value of Debentures   104,469,000   104,200,000  
Remaining discounts on acquired Debentures   25,400,000   $ 25,700,000  
Trust Preferred Securities Subject to Mandatory Redemption          
Subordinated Borrowing [Line Items]          
Amount of pooled trust preferred securities issued   $ 126,000,000      
Percent included in tier one capital, maximum   25.00%      
Excess of percent threshold included in tier two capital   25.00%      
Convertible Notes          
Subordinated Borrowing [Line Items]          
Aggregate principal amount issued   $ 217,500,000     $ 217,500,000
Interest rate         2.00%
Initial conversion rate 0.0450760 0.0450760      
Initial conversion price (in dollars per share) | $ / shares $ 22.18        
Premium percentage to closing stock price on date of pricing of the notes 22.50%        
Call option, percentage of principal amount in cash 100.00%        
Repurchase or put option, percentage of principal amount in cash 100.00%        
Interest expense on convertible notes   $ 1,300,000 $ 2,300,000    
Number of outstanding years for which non-cash interest expense and issuance cost capitalization expense will be recorded 5 years 5 years   5 years  
Convertible Notes | Discount Rate          
Subordinated Borrowing [Line Items]          
Discount rate 0.0425