Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Basic:
Income from continuing operations less noncontrolling interest	$ 9,302		$ 9,764		$ 63,718		$ 68,758		$ 45,480	$ 60,833	$ 78,691	$ 51,562	$ 151,542	$ 236,566	$ 206,158
Income (loss) from discontinued operations, net of tax	(19,271)		1,187		3,610		1,662		(592)	(40,030)	(2,657)	8,379	(12,812)	(34,900)	180,898
Net Income Attributable to McDermott International, Inc.	(9,969)	[1]	10,951	[1]	67,328	[1]	70,420	[1]	44,888	20,803	76,034	59,941	138,730	201,666	387,056
Weighted average common shares													234,598,901	232,173,362	229,471,020
Basic earnings per common share:
Income from continuing operations less noncontrolling interest	$ 0.04		$ 0.04		$ 0.27		$ 0.29		$ 0.20	$ 0.26	$ 0.34	$ 0.22	$ 0.65	$ 1.02	$ 0.90
Income (loss) from discontinued operations, net of tax	$ (0.08)		$ 0.01		$ 0.02		$ 0.01			$ (0.17)	$ (0.01)	$ 0.04	$ (0.05)	$ (0.15)	$ 0.79
Net income attributable to McDermott International, Inc.	$ (0.04)		$ 0.05		$ 0.29		$ 0.30		$ 0.19	$ 0.09	$ 0.33	$ 0.26	$ 0.59	$ 0.87	$ 1.69
Diluted:
Income from continuing operations less noncontrolling interest	9,302		9,764		63,718		68,758		45,480	60,833	78,691	51,562	151,542	236,566	206,158
Income (loss) from discontinued operations, net of tax	(19,271)		1,187		3,610		1,662		(592)	(40,030)	(2,657)	8,379	(12,812)	(34,900)	180,898
Net Income Attributable to McDermott International, Inc.	$ (9,969)	[1]	$ 10,951	[1]	$ 67,328	[1]	$ 70,420	[1]	$ 44,888	$ 20,803	$ 76,034	$ 59,941	$ 138,730	$ 201,666	$ 387,056
Weighted average common shares (basic)													234,598,901	232,173,362	229,471,020
Effect of dilutive securities:
Stock options, restricted stock and performance shares													2,441,606	3,448,667	4,155,856
Adjusted weighted average common shares													237,040,507	235,622,029	233,626,876
Diluted earnings per common share:
Income from continuing operations less noncontrolling interest	$ 0.04		$ 0.04		$ 0.27		$ 0.29		$ 0.19	$ 0.26	$ 0.34	$ 0.22	$ 0.64	$ 1.00	$ 0.88
Income (loss) from discontinued operations, net of tax	$ (0.08)		$ 0.01		$ 0.02		$ 0.01			$ (0.17)	$ (0.01)	$ 0.04	$ (0.05)	$ (0.15)	$ 0.78
Net income attributable to McDermott International, Inc.	$ (0.04)		$ 0.05		$ 0.28		$ 0.30		$ 0.19	$ 0.09	$ 0.32	$ 0.26	$ 0.59	$ 0.85	$ 1.66

[1] See Note 2 for discussion on discontinued operations and other items.