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Debt - Narratives (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Feb. 12, 2019
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
May 23, 2016
Line of Credit Facility          
Line of credit maximum borrowing amount   $ 300,000      
Debt amortization expense   36 $ 46    
Long-term Line of Credit, Noncurrent   $ 50,000   $ 50,000  
Line of Credit | Revolving Credit Facility Due 2024          
Line of Credit Facility          
Debt instrument, term 5 years        
Line of credit maximum borrowing amount $ 300,000     $ 300,000 $ 300,000
Line of credit facility contingent increase to maximum borrowing capacity 150,000        
Commitment fee percentage per annum   0.20%   0.20%  
Long-term Line of Credit, Noncurrent   $ 50,000      
Line of Credit | Revolving Credit Facility Due 2024 Swingline Sublimit          
Line of Credit Facility          
Line of credit maximum borrowing amount 15,000        
Line of Credit | Revolving Credit Facility Due 2024 Letter Of Credit Sublimit          
Line of Credit Facility          
Line of credit maximum borrowing amount $ 10,000        
Minimum | Line of Credit | Revolving Credit Facility Due 2024          
Line of Credit Facility          
Commitment fee percentage per annum 0.20%        
Maximum | Line of Credit | Revolving Credit Facility Due 2024          
Line of Credit Facility          
Commitment fee percentage per annum 0.30%