Schedule of Segment Reporting Information, Revenue by Vessel Class (Detail) - USD ($)
$ in Thousands

1 Months Ended

2 Months Ended

3 Months Ended

4 Months Ended

6 Months Ended

Jul. 31, 2017

Sep. 30, 2017

Sep. 30, 2016

Jul. 31, 2017

Sep. 30, 2016

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 70,571

Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 34,340

$ 139,361

$ 146,597

$ 301,791

Americas Fleet Deepwater vessels

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 9,798

Percentage of revenue

14.00%

Americas Fleet Deepwater vessels | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 4,304

$ 37,270

$ 21,617

$ 77,657

Percentage of revenue

12.00%

27.00%

15.00%

26.00%

Americas Fleet Towing-Supply/supply

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 5,572

Percentage of revenue

8.00%

Americas Fleet Towing-Supply/supply | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 3,747

$ 13,039

$ 15,021

$ 29,918

Percentage of revenue

11.00%

9.00%

10.00%

Americas Fleet Other

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 2,079

Percentage of revenue

3.00%

Americas Fleet Other | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 910

$ 2,816

$ 4,210

$ 6,158

Percentage of revenue

3.00%

2.00%

3.00%

2.00%

Americas Fleet

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 17,449

Percentage of revenue

25.00%

Americas Fleet | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 8,961

$ 53,125

$ 40,848

$ 113,733

Percentage of revenue

26.00%

38.00%

28.00%

38.00%

Middle East/Asia Pacific Fleet Deepwater vessels

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 5,726

Percentage of revenue

8.00%

Middle East/Asia Pacific Fleet Deepwater vessels | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 2,667

$ 8,860

$ 13,368

$ 17,488

Percentage of revenue

8.00%

6.00%

9.00%

6.00%

Middle East/Asia Pacific Fleet Towing-Supply/supply

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 10,943

Percentage of revenue

16.00%

Middle East/Asia Pacific Fleet Towing-Supply/supply | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 5,880

$ 20,724

$ 22,945

$ 44,219

Percentage of revenue

17.00%

15.00%

16.00%

14.00%

Middle East/Asia Pacific Fleet

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 16,669

Percentage of revenue

24.00%

Middle East/Asia Pacific Fleet | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 8,547

$ 29,584

$ 36,313

$ 61,707

Percentage of revenue

25.00%

21.00%

25.00%

20.00%

Africa/Europe Fleet Deepwater vessels

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 17,582

Percentage of revenue

25.00%

Africa/Europe Fleet Deepwater vessels | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 7,588

$ 24,305

$ 29,746

$ 57,594

Percentage of revenue

22.00%

17.00%

20.00%

19.00%

Africa/Europe Fleet Towing-Supply/supply

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 15,049

Percentage of revenue

21.00%

Africa/Europe Fleet Towing-Supply/supply | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 8,124

$ 25,934

$ 35,143

$ 53,851

Percentage of revenue

24.00%

19.00%

24.00%

18.00%

Africa And Europe Fleet Other

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 3,822

Percentage of revenue

5.00%

Africa And Europe Fleet Other | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 1,120

$ 6,413

$ 4,547

$ 14,906

Percentage of revenue

3.00%

5.00%

3.00%

5.00%

Africa/Europe Fleet

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 36,453

Percentage of revenue

51.00%

Africa/Europe Fleet | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 16,832

$ 56,652

$ 69,436

$ 126,351

Percentage of revenue

49.00%

41.00%

47.00%

42.00%

Worldwide Fleet Deepwater vessels

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 33,106

Percentage of revenue

47.00%

Worldwide Fleet Deepwater vessels | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 14,559

$ 70,435

$ 64,731

$ 152,739

Percentage of revenue

42.00%

50.00%

44.00%

51.00%

Worldwide Fleet Towing-Supply/supply

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 31,564

Percentage of revenue

45.00%

Worldwide Fleet Towing-Supply/supply | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 17,751

$ 59,697

$ 73,109

$ 127,988

Percentage of revenue

52.00%

43.00%

50.00%

42.00%

Worldwide Fleet Other

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 5,901

Percentage of revenue

8.00%

Worldwide Fleet Other | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 2,030

$ 9,229

$ 8,757

$ 21,064

Percentage of revenue

6.00%

7.00%

6.00%

7.00%

Worldwide Fleet

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 70,571

Percentage of revenue

100.00%

Worldwide Fleet | Predecessor

Segment and Geographic Distribution of Operations [Line Items]

Vessel revenues

$ 34,340

$ 139,361

$ 146,597

$ 301,791

Percentage of revenue

100.00%