Summary of Impairments (Detail) $ in Thousands	1 Months Ended	3 Months Ended	4 Months Ended	5 Months Ended	12 Months Ended
Jul. 31, 2017 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jul. 31, 2017 USD ($) Vessel	Dec. 31, 2017 USD ($) Vessel	Dec. 31, 2019 USD ($) Vessel	Dec. 31, 2018 USD ($) Vessel
Asset Impairment Charges [Abstract]
Number of vessels impaired during the period \| Vessel										79	5	35	56
Amount of impairment and other expense incurred \| $	$ 21,325	$ 32,549	$ 5,224	$ 36,878	$ 16,853	$ 1,215	$ 6,186	$ 16,777	$ 163,423	$ 184,748	$ 16,777	$ 37,773	$ 61,132

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2420-110228

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration