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Subsequent Events (Unaudited) - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent Event [Line Items]
Cash proceeds from sale of assets		$ 80,000	$ 200,000	$ 850,000
Assumed debt			$ 350,000
Subsequent Event [Member] | Magellan Offshore Services Ltd [Member] | Marine Equipment [Member]
Subsequent Event [Line Items]
Sale of assets	$ 1,600,000
Cash proceeds from sale of assets	1,000,000
Gain on sale of assets	1,500,000
Subsequent Event [Member] | Magellan Offshore Services Ltd [Member] | Marine Equipment [Member] | Debt [Member]
Subsequent Event [Line Items]
Assumed debt	$ 600,000

X

- Definition

Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation.

+ References

No definition available.

+ Details

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Period Type:	instant

X

- Definition

Amount of gain (loss) on sale or disposal of assets, including but not limited to property plant and equipment, intangible assets and equity in securities of subsidiaries or equity method investee.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2443-110228

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X

- Definition

Amount of noncash consideration received for selling an asset or business through a noncash (or part noncash) transaction.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

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X

- Definition

The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

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X

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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- Details

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X

- Details

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X

- Details

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