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Credit Facility (Details)
3 Months Ended
Feb. 02, 2016
USD ($)
Mar. 31, 2018
USD ($)
Mar. 31, 2017
USD ($)
Line of Credit Facility [Line Items]      
Maximum borrowing capacity $ 100,000,000    
Debt covenant, maximum debt to total capitalization ratio 0.35    
Outstanding balance on credit facility   $ 0 $ 0
Interest expense incurred   $ 0 $ 0
Revolving Credit Facility [Member]      
Line of Credit Facility [Line Items]      
Maximum borrowing capacity $ 50,000,000    
Credit agreement term 4 years    
Letter of Credit      
Line of Credit Facility [Line Items]      
Maximum borrowing capacity $ 20,000,000    
Swing Line of Credit      
Line of Credit Facility [Line Items]      
Maximum borrowing capacity $ 5,000,000