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Long-Term Debt - Senior Notes - Additional Information (Details) - USD ($)
1 Months Ended 12 Months Ended
Dec. 31, 2015
Nov. 30, 2015
Dec. 31, 2018
Dec. 31, 2017
Debt Instrument [Line Items]        
Long term debt     $ 349,264,000 $ 348,888,000
Senior Notes        
Debt Instrument [Line Items]        
Long term debt $ 350,000,000      
Stated interest rate 3.64%   3.64%  
Debt instrument, term 5 years   5 years  
Cash proceeds from interest rate hedge   $ 4,600,000