Supplemental Selected Quarterly Financial Data (Unaudited) - Supplemental Selected Quarterly Financial Data (Unaudited) (Narrative) (Detail) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2017 USD ($) Vessel $ / shares	Dec. 31, 2016 USD ($) Vessel	Dec. 31, 2015 USD ($)
Quarterly Financial Information [Line Items]
Number of Vessels Stacked \| Vessel		42.8	41.3
Average Number of MPSVs Stacked \| Vessel		0.8	0
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount \| $	$ 125,225	$ (125,225)	$ 0	$ 0
Net Income (loss) excluding one time tax item \| $	$ (17,281)	$ (82,687)
Earnings per share diluted excluding one time tax item \| $ / shares	$ (0.47)	$ (2.24)

Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, attributable to increase (decrease) in the income tax rates.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e32059-109318

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration