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Corporate Borrowings - Narrative (Details) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Dec. 31, 2017
Feb. 14, 2020
Debt Instrument [Line Items]        
Outstanding borrowings under credit facility $ 53,590,000 $ 1,000    
Credit Agreement Due 2022        
Debt Instrument [Line Items]        
Maximum borrowing capacity 150,000,000      
Outstanding borrowings under credit facility 0 300,000    
Prudential Note Purchase Agreement, 3.53% (fixed rate) due 2027 | Senior Notes        
Debt Instrument [Line Items]        
Term loan face value 75,000,000      
Proceeds from issuance of debt     $ 20,000,000  
Prudential Note Purchase Agreement, 3.80% (fixed rate) due 2029 | Senior Notes        
Debt Instrument [Line Items]        
Proceeds from issuance of debt   20,000,000    
Credit Agreement Due 2025        
Debt Instrument [Line Items]        
Outstanding borrowings under credit facility 55,000,000 $ 0   $ 300,000
Contingent increase in borrowing capacity 100,000,000      
Payments of debt issuance costs 1,148,000      
Credit facility, remaining borrowing capacity $ 245,000,000