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Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Details) - USD ($)
$ in Thousands
Jan. 01, 2018
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Retained earnings   $ 2,306 $ 57,225 $ 3,405 $ 43,833
Accumulated other comprehensive loss   $ (21,683) $ (21,791) $ (19,294)  
ASU 2014-09          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Pre-tax impact to retained earnings $ 4,378        
Cumulative impact to retained earnings 3,319        
ASU 2018-02 | New Accounting Pronouncement, Early Adoption, Effect          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Retained earnings (593)        
Accumulated other comprehensive loss $ 593