Schedule of Segment Reporting Information, Revenue by Vessel Class (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 264,131	$ 390,952	$ 562,444	$ 772,462
Americas Fleet Deepwater vessels
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 61,776	$ 91,403	$ 141,928	$ 173,685
Percentage of revenue	24.00%	23.00%	25.00%	23.00%
Americas Fleet Towing-Supply/supply
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 24,121	$ 34,387	$ 53,636	$ 63,904
Percentage of revenue	9.00%	9.00%	9.00%	8.00%
Americas Fleet Other
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 3,313	$ 8,223	$ 7,818	$ 16,407
Percentage of revenue	1.00%	2.00%	2.00%	2.00%
Americas Fleet
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 89,210	$ 134,013	$ 203,382	$ 253,996
Percentage of revenue	34.00%	34.00%	36.00%	33.00%
Asia and Pacific Fleet Deepwater vessels
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 23,435	$ 27,675	$ 43,268	$ 51,917
Percentage of revenue	9.00%	7.00%	8.00%	7.00%
Asia/Pacific Fleet Towing-Supply/supply
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 8,738	$ 17,338	$ 16,842	$ 32,375
Percentage of revenue	3.00%	5.00%	3.00%	4.00%
Asia and Pacific Fleet Other
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues		$ 976		$ 1,946
Asia and Pacific Fleet Other \| Maximum
Segment and Geographic Distribution of Operations [Line Items]
Percentage of revenue		1.00%		1.00%
Asia/Pacific Fleet
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 32,173	$ 45,989	$ 60,110	$ 86,238
Percentage of revenue	12.00%	12.00%	11.00%	11.00%
Middle East/North Africa Fleet Deepwater vessels
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 20,769	$ 19,254	$ 41,155	$ 38,721
Percentage of revenue	8.00%	5.00%	7.00%	5.00%
Middle East/North Africa Fleet Towing-Supply/supply
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 23,914	$ 28,715	$ 50,103	$ 63,994
Percentage of revenue	9.00%	7.00%	9.00%	9.00%
Middle East and North Africa Fleet Other
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 653	$ 868	$ 1,344	$ 1,661
Percentage of revenue			1.00%
Middle East and North Africa Fleet Other \| Maximum
Segment and Geographic Distribution of Operations [Line Items]
Percentage of revenue	1.00%	1.00%		1.00%
Middle East/North Africa fleet
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 45,336	$ 48,837	$ 92,602	$ 104,376
Percentage of revenue	17.00%	12.00%	16.00%	14.00%
Sub-Saharan Africa/Europe Fleet Deepwater vessels
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 39,955	$ 89,193	$ 93,921	$ 180,884
Percentage of revenue	15.00%	23.00%	17.00%	23.00%
Sub-Saharan Africa/Europe Fleet Towing-Supply/supply
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 42,106	$ 54,617	$ 83,304	$ 110,053
Percentage of revenue	16.00%	14.00%	15.00%	14.00%
Sub Saharan Africa And Europe Fleet Other
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 15,351	$ 18,303	$ 29,125	$ 36,915
Percentage of revenue	6.00%	5.00%	5.00%	5.00%
Sub-Saharan Africa/Europe Fleet
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 97,412	$ 162,113	$ 206,350	$ 327,852
Percentage of revenue	37.00%	42.00%	37.00%	42.00%
Worldwide Fleet Deepwater vessels
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 145,935	$ 227,525	$ 320,272	$ 445,207
Percentage of revenue	56.00%	58.00%	57.00%	58.00%
Worldwide Fleet Towing-Supply/supply
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 98,879	$ 135,057	$ 203,885	$ 270,326
Percentage of revenue	37.00%	35.00%	36.00%	35.00%
Worldwide Fleet Other
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 19,317	$ 28,370	$ 38,287	$ 56,929
Percentage of revenue	7.00%	7.00%	7.00%	7.00%
Worldwide Fleet
Segment and Geographic Distribution of Operations [Line Items]
Vessel revenues	$ 264,131	$ 390,952	$ 562,444	$ 772,462
Percentage of revenue	100.00%	100.00%	100.00%	100.00%