Commitments and contingencies (Details) € in Millions, $ in Millions	Dec. 31, 2020 USD ($) € / $	Dec. 31, 2020 EUR (€) € / $
Commitments Under Long-Term Lease Contracts [Abstract]
Future minimum contracted lease payments due within next 12 months \| $	$ 6.8
Purchase Commitment for Ballast Water Management Systems [Member]
Commitments Under Contracts for BWMS Installation [Abstract]
Contractual purchase obligations	$ 0.8	€ 0.7
Exchange rate \| € / $	0.8149	0.8149

Foreign exchange rate used to translate amounts denominated in functional currency to reporting currency.

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Amount of lease payment to be received by lessor for operating lease in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Minimum amount to be expended to satisfy the terms of arrangements in which the entity has agreed to expend funds to procure goods or services, excluding long-term purchase commitments or unconditional purchase obligations.

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