Computation of Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Share data	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Basic:
Income from continuing operations less noncontrolling interests	$ 9,764		$ 60,833		$ 142,240		$ 191,086
Income (loss) from discontinued operations, net of tax	1,187		(40,030)		6,459		(34,308)
Net income attributable to McDermott International, Inc.	10,951		20,803		148,699		156,778
Weighted average common shares	234,940,184		232,670,579		234,451,430		231,780,675
Income from continuing operations less noncontrolling interests	$ 0.04		$ 0.26		$ 0.61		$ 0.82
Income (loss) from discontinued operations, net of tax	$ 0.01		$ (0.17)		$ 0.03		$ (0.15)
Net income attributable to McDermott International, Inc.	$ 0.05		$ 0.09		$ 0.63		$ 0.67
Diluted:
Income from continuing operations less noncontrolling interests	9,764		60,833		142,240		191,086
Income (loss) from discontinued operations, net of tax	1,187		(40,030)		6,459		(34,308)
Net income attributable to McDermott International, Inc.	$ 10,951		$ 20,803		$ 148,699		$ 156,778
Weighted average common shares (basic)	234,940,184		232,670,579		234,451,430		231,780,675
Effect of dilutive securities:
Stock options, restricted stock and restricted stock units	2,007,479	[1]	3,600,832	[1]	2,627,875	[1]	3,368,656	[1]
Adjusted weighted average common shares and assumed exercises of stock options and vesting of stock awards	236,947,663		236,271,411		237,079,305		235,149,331
Income from continuing operations less noncontrolling interests	$ 0.04		$ 0.26		$ 0.60		$ 0.81
Income (loss) from discontinued operations, net of tax	$ 0.01		$ (0.17)		$ 0.03		$ (0.14)
Net income attributable to McDermott International, Inc.	$ 0.05		$ 0.09		$ 0.63		$ 0.67

[1] Approximately 0.6 million and 1.7 million and 0.5 million and 2.5 million shares underlying outstanding stock-based awards for the three-month and nine-month periods ended September 30, 2011 and 2010, respectively, were excluded from the computation of diluted earnings per share because they were antidilutive.