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Borrowings - Narrative (Details) - USD ($)
1 Months Ended 3 Months Ended 6 Months Ended
Jun. 01, 2022
Jun. 01, 2012
Mar. 31, 2024
Jan. 31, 2010
Mar. 31, 2024
Dec. 31, 2023
Mar. 31, 2023
Mar. 31, 2024
Mar. 31, 2023
Oct. 12, 2023
Sep. 30, 2023
Oct. 13, 2022
Line of Credit Facility [Abstract]                        
Loss on extinguishment of debt, net         $ 424,000   $ 0 $ 437,000 $ 515,000      
Senior Notes                        
Line of Credit Facility [Abstract]                        
Aggregate principal amount of debt     $ 250,000,000   250,000,000     250,000,000        
Junior Subordinated Notes [Abstract]                        
Aggregate principal amount of debt     250,000,000   250,000,000     250,000,000        
6.750% | Senior Notes                        
Line of Credit Facility [Abstract]                        
Extinguishment of debt     197,900,000     $ 4,300,000            
Loss on extinguishment of debt, net     400,000     $ 100,000            
Junior Subordinated Notes                        
Junior Subordinated Notes [Abstract]                        
Aggregate principle balance of notes     $ 100,800,000   $ 100,800,000     $ 100,800,000        
Weighted average fixed interest rate of debt     8.03%   8.03%     8.03%        
Junior Subordinated Debt, Modified Terms                        
Line of Credit Facility [Abstract]                        
Aggregate principal amount of debt       $ 75,000,000                
Junior Subordinated Notes [Abstract]                        
Aggregate principal amount of debt       $ 75,000,000                
Redemption price percentage   75.00%                    
Annual increase of percentage of principal amount redeemable 1.785%                      
Junior Subordinated Debt, Modified Terms | LIBOR                        
Junior Subordinated Notes [Abstract]                        
Variable rate floor       4.25%                
Variable rate cap       9.25%                
Junior Subordinated Debt, Original Terms                        
Line of Credit Facility [Abstract]                        
Aggregate principal amount of debt     $ 25,800,000   $ 25,800,000     $ 25,800,000        
Junior Subordinated Notes [Abstract]                        
Aggregate principal amount of debt     25,800,000   25,800,000     $ 25,800,000        
Junior Subordinated Debt, Original Terms | LIBOR                        
Junior Subordinated Notes [Abstract]                        
Basis spread on variable rate       2.71%       2.45%        
Senior Unsecured Revolving Credit Facility                        
Line of Credit Facility [Abstract]                        
Credit facility, maximum borrowing capacity                       $ 400,000,000
Credit facility, available increase in borrowing capacity                       $ 100,000,000
Senior Unsecured Revolving Credit Facility     0   0     $ 0     $ 0  
Letters of credit secured using cash collateral     0   0     0        
Amount of available borrowings under the secured revolving credit facility     300,000,000   300,000,000     300,000,000        
Senior Unsecured Revolving Credit Facility | Senior Notes                        
Line of Credit Facility [Abstract]                        
Credit facility, maximum borrowing capacity                   $ 300,000,000    
Letter of Credit                        
Line of Credit Facility [Abstract]                        
Letters of credit secured using cash collateral     $ 34,800,000   $ 34,800,000     $ 34,800,000     $ 31,200,000  
Letter of Credit | Senior Notes                        
Line of Credit Facility [Abstract]                        
Credit facility, maximum borrowing capacity                   $ 100,000,000