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Debt (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Apr. 27, 2018
Apr. 26, 2018
Oct. 29, 2015
May 09, 2013
Line of Credit Facility [Line Items]            
Unsecured revolving line of credit           $ 50,000,000.0
Ratio of consolidated indebtedness to earnings before interest, taxes, depreciation and amortization, maximum allowed 3.25          
Ratio of consolidated earnings before interest, taxes, depreciation and amortization expense, minimum allowed 3.00          
Interest rate in event of default 2.00%          
First Amendment            
Line of Credit Facility [Line Items]            
Unsecured revolving line of credit         $ 125,000,000.0  
Optional credit line increase         $ 25,000,000.0  
Second Amendment            
Line of Credit Facility [Line Items]            
Unsecured revolving line of credit     $ 5,000,000.0 $ 125,000,000.0    
Letter of credit sublimit     $ 5,000,000.0 $ 10,000,000.0    
Revolving Line of Credit            
Line of Credit Facility [Line Items]            
Outstanding borrowing on line of credit $ 0          
Interest expense $ 0 $ 0        
Weighted average interest rate 3.00% 3.60%        
Minimum            
Line of Credit Facility [Line Items]            
Quarterly commitment fee 0.175%          
Maximum            
Line of Credit Facility [Line Items]            
Quarterly commitment fee 0.30%          
Base Rate | Minimum            
Line of Credit Facility [Line Items]            
Variable interest rate spread 0.00%          
Base Rate | Maximum            
Line of Credit Facility [Line Items]            
Variable interest rate spread 0.50%          
London Interbank Offered Rate | Minimum            
Line of Credit Facility [Line Items]            
Variable interest rate spread 1.125%          
London Interbank Offered Rate | Maximum            
Line of Credit Facility [Line Items]            
Variable interest rate spread 2.00%