Computation of Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Earnings Per Share Disclosure [Line Items]
Income from continuing operations less noncontrolling interests	$ 50,612		$ 9,764		$ 162,612		$ 142,240
Income from discontinued operations, net of tax			1,187		3,497		6,459
Net income attributable to McDermott International, Inc.	$ 50,612		$ 10,951		$ 166,109		$ 148,699
Weighted average common shares (basic)	235,817,203		234,940,184		235,568,889		234,451,430
Effect of dilutive securities:
Stock options, restricted stock and restricted stock units	2,049,797	[1]	2,007,479	[1]	1,984,574	[1]	2,627,875	[1]
Adjusted weighted average common shares and assumed exercises of stock options and vesting of stock awards (diluted)	237,867,000		236,947,663		237,553,463		237,079,305
Basic earnings per share:
Income from continuing operations less noncontrolling interests	$ 0.21		$ 0.04		$ 0.69		$ 0.61
Income from discontinued operations, net of tax			$ 0.01		$ 0.01		$ 0.03
Net income attributable to McDermott International, Inc.	$ 0.21		$ 0.05		$ 0.70		$ 0.63
Diluted earnings per share:
Income from continuing operations less noncontrolling interests	$ 0.21		$ 0.04		$ 0.68		$ 0.60
Income from discontinued operations, net of tax			$ 0.01		$ 0.01		$ 0.03
Net income attributable to McDermott International, Inc.	$ 0.21		$ 0.05		$ 0.69		$ 0.63

[1] Approximately 1.7 million and 1.8 million shares underlying outstanding stock-based awards were excluded from the computation of diluted earnings per share because they were antidilutive for the three-month and nine-month periods ended September 30, 2012, respectively. Approximately 0.6 million and 1.7 million shares underlying outstanding stock-based awards were excluded from the computation of diluted earnings per share for each of the three-month and nine-month periods ended September 30, 2011.