Selected Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	2 Months Ended	3 Months Ended						4 Months Ended		5 Months Ended		9 Months Ended	12 Months Ended
	Jul. 31, 2017	Sep. 30, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Jul. 31, 2017		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2018		Mar. 31, 2017
Quarterly Financial Data [Line Items]
Revenues		$ 74,300	$ 110,234	$ 99,192	$ 105,601	$ 91,493	$ 104,453
Impairment of due from affiliate			(20,083)											$ (20,083)
Asset impairments included in operating loss			(36,878)	(16,853)	(1,215)	(6,186)	(16,777)				$ (16,777)	[1]		(61,132)	[1]
Operating income (loss)		(5,782)	(70,077)	(25,086)	(140)	(12,194)	(18,091)				(23,873)			(107,497)
Net loss attributable to Tidewater Inc.		$ (15,693)	$ (90,509)	$ (30,896)	$ (10,940)	$ (39,172)	$ (23,573)				$ (39,266)			$ (171,517)
Basic loss per share attributable to Tidewater Inc.		$ (0.81)	$ (2.83)	$ (1.16)	$ (0.44)	$ (1.67)	$ (1.02)				$ (1.82)	[2]		$ (6.45)	[2]
Diluted loss per share attributable to Tidewater Inc.		$ (0.81)	$ (2.83)	$ (1.16)	$ (0.44)	$ (1.67)	$ (1.02)				$ (1.82)	[3]		$ (6.45)	[3]
Predecessor
Quarterly Financial Data [Line Items]
Revenues	$ 36,263							$ 115,106
Asset impairments included in operating loss	(21,325)							(163,423)	$ (184,748)	[1]						$ (484,727)	[1]
Operating income (loss)	(38,674)							(205,374)	(244,048)				$ (508,513)			(577,853)
Net loss attributable to Tidewater Inc.	$ (1,122,475)							$ (524,434)	$ (1,646,909)				$ (565,263)			$ (660,118)
Basic loss per share attributable to Tidewater Inc.	$ (23.82)							$ (11.13)	$ (34.95)	[2]			$ (12.01)			$ (14.02)	[2]
Diluted loss per share attributable to Tidewater Inc.	$ (23.82)							$ (11.13)	$ (34.95)	[3]			$ (12.01)			$ (14.02)	[3]

[1] The twelve months ended December 31, 2018, the period August 1, 2017 through December 31, 2017 and the twelve months ended March 31, 2017 included $3.5 million, $2.3 million and $2.2 million respectively, of impairments related to inventory and other non-vessel assets. There were no impairments to non-vessel assets during the period April 1, 2017 through July 31, 2017.

[2] We calculate “Loss per share, basic” by dividing “Net loss available to common shareholders” by “Weighted average outstanding share of common stock, basic”.

[3] We calculate “Loss per share, diluted” by dividing “Net loss available to common shareholders” by “Weighted average common stock and equivalents”.