For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Summary of Significant Accounting Policies - Major Charterers (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Hyundai Merchant Marine Co., Ltd.
Entity Wide Revenue Major Customer [Line Items]
Customer revenue percentage	24.50%	26.80%	29.60%
Yang Ming Marine Transport Corporation
Entity Wide Revenue Major Customer [Line Items]
Customer revenue percentage		12.00%	13.00%
MediterraneanShipping Co. S.A.
Entity Wide Revenue Major Customer [Line Items]
Customer revenue percentage			11.60%