Segment Information, Geographical Data and Major Customers (Detail) - USD ($)		3 Months Ended			6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018		Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Total revenues		$ 125,859,000	$ 105,601,000		$ 248,008,000	$ 197,094,000
Operating profit (loss)	[1]	8,321,000	7,647,000		12,632,000	6,504,000
Corporate expenses	[1],[2]	(12,221,000)	(7,910,000)		(27,422,000)	(14,694,000)
Gain (loss) on asset dispositions, net		(494,000)	1,338,000		776,000	3,257,000
Asset impairments		0	(1,215,000)	[3]	0	(7,401,000)	[3]
Operating loss		(4,394,000)	(140,000)		(14,014,000)	(12,334,000)
Depreciation and amortization		25,038,000	12,785,000		47,970,000	24,802,000
Additions to properties and equipment		5,757,000	4,097,000		8,873,000	5,775,000
All Other Segments
Segment Reporting Information [Line Items]
Operating profit (loss)	[1]	1,625,000	778,000		3,330,000	2,284,000
Depreciation and amortization		5,000	5,000		10,000	10,000
Operating Segments | Americas
Segment Reporting Information [Line Items]
Operating profit (loss)	[1]	2,900,000	5,681,000		1,870,000	10,592,000
Depreciation and amortization		6,515,000	3,530,000		12,776,000	6,843,000
Additions to properties and equipment		206,000	1,230,000		604,000	2,267,000
Operating Segments | Middle East/Asia Pacific
Segment Reporting Information [Line Items]
Operating profit (loss)	[1]	(2,127,000)	625,000		(3,289,000)	(1,628,000)
Depreciation and amortization		5,319,000	2,844,000		9,769,000	5,613,000
Additions to properties and equipment		2,180,000	1,073,000		3,639,000	1,496,000
Operating Segments | Europe/Mediterranean Sea
Segment Reporting Information [Line Items]
Operating profit (loss)	[1]	2,824,000	(1,142,000)		(493,000)	(4,696,000)
Depreciation and amortization		7,741,000	2,239,000		15,187,000	4,043,000
Additions to properties and equipment		601,000	135,000		722,000	135,000
Operating Segments | West Africa Segment
Segment Reporting Information [Line Items]
Operating profit (loss)	[1]	3,099,000	1,705,000		11,214,000	(48,000)
Depreciation and amortization		5,100,000	4,067,000		9,543,000	8,093,000
Additions to properties and equipment		1,340,000			1,583,000	1,000
Corporate
Segment Reporting Information [Line Items]
Depreciation and amortization		358,000	100,000		685,000	200,000
Additions to properties and equipment		1,430,000	1,659,000		2,325,000	1,876,000
Service | Operating Segments | Americas
Segment Reporting Information [Line Items]
Total revenues		35,199,000	32,601,000		70,477,000	58,682,000
Service | Operating Segments | Middle East/Asia Pacific
Segment Reporting Information [Line Items]
Total revenues		20,449,000	22,406,000		40,905,000	40,794,000
Service | Operating Segments | Europe/Mediterranean Sea
Segment Reporting Information [Line Items]
Total revenues		35,027,000	13,357,000		63,585,000	22,980,000
Service | Operating Segments | West Africa Segment
Segment Reporting Information [Line Items]
Total revenues		32,966,000	35,810,000		68,336,000	69,212,000
Other Operating Revenues
Segment Reporting Information [Line Items]
Total revenues		$ 2,218,000	$ 1,427,000		$ 4,705,000	$ 5,426,000

[1] Prior to January 1, 2019, we allocated the costs of certain marine operations related to general and administrative functions, such as marine management, engineering, supply chain management, risk management, fleet human resources and health and safety to the segment general and administrative expenses.  Beginning on January 1, 2019 our management elected to modify that process in order to better analyze costs and better align the policies of the two combined companies such that all costs related to those previously allocated functions will remain as corporate general and administrative expenses. This explains the significant increase in corporate expenses that is reflected in the table above for the three and six months ended June 30, 2019.   

[2] Included in corporate expenses for both the three and six months ended June 30, 2019 was $0.5 million and $4.2 million, respectively, of integration costs related to the business combination with GulfMark.

[3] Refer to Note (14) for additional information regarding asset impairment charges.