Schedule of Segment Reporting Information, Revenue by Vessel Class (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 139,361	$ 264,131	$ 301,791	$ 562,444
Americas Fleet Deepwater vessels
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 37,270	$ 61,776	$ 77,657	$ 141,928
Percentage of revenue	27.00%	24.00%	26.00%	25.00%
Americas Fleet Towing-Supply/supply
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 13,039	$ 24,121	$ 29,918	$ 53,636
Percentage of revenue	9.00%	9.00%	10.00%	9.00%
Americas Fleet Other
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 2,816	$ 3,313	$ 6,158	$ 7,818
Percentage of revenue	2.00%	1.00%	2.00%	2.00%
Americas Fleet
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 53,125	$ 89,210	$ 113,733	$ 203,382
Percentage of revenue	38.00%	34.00%	38.00%	36.00%
Asia and Pacific Fleet Deepwater vessels
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 1,872	$ 23,435	$ 4,462	$ 43,268
Percentage of revenue	1.00%	9.00%	2.00%	8.00%
Asia/Pacific Fleet Towing-Supply/supply
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 4,238	$ 8,738	$ 9,569	$ 16,842
Percentage of revenue	3.00%	3.00%	3.00%	3.00%
Asia/Pacific Fleet
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 6,110	$ 32,173	$ 14,031	$ 60,110
Percentage of revenue	4.00%	12.00%	5.00%	11.00%
Middle East Fleet Deepwater vessels
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 6,988	$ 5,750	$ 13,026	$ 12,441
Percentage of revenue	5.00%	2.00%	4.00%	2.00%
Middle East Fleet Towing-Supply/supply
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 16,486	$ 22,934	$ 34,650	$ 48,496
Percentage of revenue	12.00%	9.00%	11.00%	9.00%
Middle East fleet
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 23,474	$ 28,684	$ 47,676	$ 60,937
Percentage of revenue	17.00%	11.00%	15.00%	11.00%
Africa/Europe Fleet Deepwater vessels
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 24,305	$ 54,974	$ 57,594	$ 122,635
Percentage of revenue	17.00%	21.00%	19.00%	22.00%
Africa/Europe Fleet Towing-Supply/supply
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 25,934	$ 43,086	$ 53,851	$ 84,911
Percentage of revenue	19.00%	16.00%	18.00%	15.00%
Africa And Europe Fleet Other
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 6,413	$ 16,004	$ 14,906	$ 30,469
Percentage of revenue	5.00%	6.00%	5.00%	5.00%
Africa/Europe Fleet
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 56,652	$ 114,064	$ 126,351	$ 238,015
Percentage of revenue	41.00%	43.00%	42.00%	42.00%
Worldwide Fleet Deepwater vessels
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 70,435	$ 145,935	$ 152,739	$ 320,272
Percentage of revenue	50.00%	56.00%	51.00%	57.00%
Worldwide Fleet Towing-Supply/supply
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 59,697	$ 98,879	$ 127,988	$ 203,885
Percentage of revenue	43.00%	37.00%	42.00%	36.00%
Worldwide Fleet Other
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 9,229	$ 19,317	$ 21,064	$ 38,287
Percentage of revenue	7.00%	7.00%	7.00%	7.00%
Worldwide Fleet
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 139,361	$ 264,131	$ 301,791	$ 562,444
Percentage of revenue	100.00%	100.00%	100.00%	100.00%