Operating Leases (Detail) $ in Millions	Dec. 31, 2016 USD ($) vessel	Dec. 31, 2015 USD ($)
Operating Leased Assets [Line Items]
Minimum commitment to be incurred by Company, 2017	$ 26.8
Minimum commitment to be incurred by Company, 2018	8.3
Minimum commitment to be incurred by Company, 2019	8.3
Minimum commitment to be incurred by Company, 2020	8.3
Minimum commitment to be incurred by Company, 2021	1.4
Minimum scheduled future revenues to be received by Company	136.5
Minimum scheduled future revenues to be received by Company in current year	93.4
Minimum scheduled future revenues to be received by Company in second year	40.5
Minimum scheduled future revenues to be received by Company in third year	2.6
Carrying amount of vessels employed on operating leases	471.7	$ 442.5
Cost of the vessels	683.2	596.7
Accumulated depreciation of the vessels	$ 211.5	$ 154.2
Charters In [Member]
Operating Leased Assets [Line Items]
Number of vessels \| vessel	7
Charters In [Member] \| Commitments [Member]
Operating Leased Assets [Line Items]
Number of vessels \| vessel	9
Charters In [Member] \| Commitments [Member] \| Ship-to-ship Support Vessel [Member]
Operating Leased Assets [Line Items]
Number of vessels \| vessel	2
Charters Out [Member]
Operating Leased Assets [Line Items]
Number of vessels \| vessel	1
Number of vessels \| vessel	13
Charters Out [Member] \| Time Charter Contract Expiration 2017 [Member]
Operating Leased Assets [Line Items]
Number of vessels \| vessel	7
Charters Out [Member] \| Time Charter Contract Expiration 2018 [Member]
Operating Leased Assets [Line Items]
Number of vessels \| vessel	6
Charters Out [Member] \| Time Charter Contract Expiration 2019 [Member]
Operating Leased Assets [Line Items]
Number of vessels \| vessel	1

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Number of vessels held under operating lease contracts.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 10
-Section 55
-Paragraph 40
-Subparagraph (Note 3)
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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
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-Subparagraph (a)
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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Future minimum rental payments in aggregate as of the balance sheet date under operating leases.

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Future rental payments receivable within one year of the balance sheet date under an operating lease.

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Future rental payments receivable within the third year from the balance sheet date under an operating lease.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Amount before accumulated depreciation of physical assets used in the normal conduct of business to produce goods and services subject to or available for lease.

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The amount of property, by major property class, net of accumulated depreciation, subject to or available for lease as of the balance sheet date.

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