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Debt - Additional Information (Details) - USD ($)
12 Months Ended
Dec. 31, 2007
Mar. 31, 2019
Dec. 31, 2018
Mortgages and Notes Payable [Member]      
Debt Instrument [Line Items]      
Weighted average interest rate   4.50%  
6.804% Trust Preferred Securities [Member]      
Debt Instrument [Line Items]      
Stated interest rate 6.804%    
Face amount of debt instrument $ 200,000,000    
Interest rate, effective percentage   4.45%  
Principal amount outstanding   $ 120,120,000 $ 120,120,000
Unamortized debt issuance costs   $ 1,799,000 $ 1,824,000
6.804% Trust Preferred Securities [Member] | London Interbank Offered Rate (LIBOR) [Member]      
Debt Instrument [Line Items]      
Basis spread on variable rate 1.70%    
Minimum [Member] | Mortgages and Notes Payable [Member]      
Debt Instrument [Line Items]      
Stated interest rate   2.20%  
Maximum [Member] | Mortgages and Notes Payable [Member]      
Debt Instrument [Line Items]      
Stated interest rate   6.50%