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Summary of Significant Accounting Policies - Concentration of Credit Risk (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Concentration Risk [Line Items]      
Other Nonoperating Income (Expense) $ 3,257 $ 2,292 $ 2,637
Provision (reversal) for doubtful accounts $ 590 $ (231) $ 3,347
CMA CGM S.A | Operating and Capital Leases Billing [Member] [Domain] | Credit Concentration Risk [Member]      
Concentration Risk [Line Items]      
Concentration Risk, Percentage 21.00% 20.00% 19.00%
Mediterranean Shipping Company [Member] | Operating and Capital Leases Billing [Member] [Domain] | Credit Concentration Risk [Member]      
Concentration Risk [Line Items]      
Concentration Risk, Percentage 14.00% 14.00% 14.00%
Mediterranean Shipping Company [Member] | Accounts Receivable [Member] | Credit Concentration Risk [Member]      
Concentration Risk [Line Items]      
Concentration Risk, Percentage 6.00% 5.00%  
CMACGN | Accounts Receivable [Member] | Credit Concentration Risk [Member]      
Concentration Risk [Line Items]      
Concentration Risk, Percentage 21.00% 29.00%  
Hanjin Shipping Co. [Member]      
Concentration Risk [Line Items]      
Other Nonoperating Income (Expense)     $ 6,800