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, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share Disclosure [Line Items]
Income from continuing operations less noncontrolling interest	$ 40,544	[1]	$ 50,612	[2]	$ 52,739	[3]	$ 59,261	$ 9,302		$ 9,764	[4]	$ 63,718	[5]	$ 68,758		$ 203,156	$ 151,542	$ 236,566
Income (loss) from discontinued operations, net of tax							3,497	(19,271)	[6]	1,187	[4],[6]	3,610	[5],[6]	1,662	[6]	3,497	(12,812)	(34,900)
Net income attributable to McDermott International, Inc.	$ 40,544	[1]	$ 50,612	[2]	$ 52,739	[3]	$ 62,758	$ (9,969)		$ 10,951	[4]	$ 67,328	[5]	$ 70,420		$ 206,653	$ 138,730	$ 201,666
Weighted average common shares (basic)																235,638,422	234,598,901	232,173,362
Effect of dilutive securities:
Stock options, restricted stock and performance shares																1,981,266	2,441,606	3,448,667
Adjusted weighted average common shares (diluted)																237,619,688	237,040,507	235,622,029
Basic earnings per common share:
Income from continuing operations less noncontrolling interest	$ 0.17	[1]	$ 0.21	[2]	$ 0.22	[3]	$ 0.25	$ 0.04		$ 0.04	[4]	$ 0.27	[5]	$ 0.29		$ 0.86	$ 0.65	$ 1.02
Income (loss) from discontinued operations, net of tax							$ 0.01	$ (0.08)		$ 0.01	[4]	$ 0.02	[5]	$ 0.01		$ 0.01	$ (0.05)	$ (0.15)
Net income attributable to McDermott International, Inc.	$ 0.17	[1]	$ 0.21	[2]	$ 0.22	[3]	$ 0.27	$ (0.04)		$ 0.05	[4]	$ 0.29	[5]	$ 0.30		$ 0.88	$ 0.59	$ 0.87
Diluted earnings per common share:
Income from continuing operations less noncontrolling interest	$ 0.17	[1]	$ 0.21	[2]	$ 0.22	[3]	$ 0.25	$ 0.04		$ 0.04	[4]	$ 0.27	[5]	$ 0.29		$ 0.86	$ 0.64	$ 1.00
Income (loss) from discontinued operations, net of tax							$ 0.01	$ (0.08)		$ 0.01	[4]	$ 0.02	[5]	$ 0.01		$ 0.01	$ (0.05)	$ (0.15)
Net income attributable to McDermott International, Inc.	$ 0.17	[1]	$ 0.21	[2]	$ 0.22	[3]	$ 0.26	$ (0.04)		$ 0.05	[4]	$ 0.28	[5]	$ 0.30		$ 0.87	$ 0.59	$ 0.85

[1] Operating income for the quarter ended December 31, 2012 was influenced by significant cost savings on marine installation activities on an EPCI project, partially offset by project losses of approximately $52.0 million recognized across each segment. Income from continuing operations, less non-controlling interests was impacted by an increase in our provision for income taxes and sales, general & administrative expenses, partially offset by an increase in gain (loss) on foreign currency - net.

[2] Revenues for the quarter ended September 30, 2012 were influenced by increased marine activity on certain of our Asia Pacific projects.

[3] Operating income for the quarter ended June 30 2012 was influenced by increased fabrication activities partially offset by lower project close-outs and settlements.

[4] Operating income for the September 30, 2011 quarter was influenced by the $75.4 million decline in the Middle East segment. The Middle East decline was primarily driven by reduced fabrication and marine activity levels, lower change orders, project close-outs and settlements on completed contracts. In addition, the September quarter was impacted by approximately $50.0 million of project charges recognized across segments.

[5] Operating income for the June 30, 2011 quarter was influenced by a $49.1 million decline in our Middle East segment as a result of reduced marine activity and the substantial completion of several higher margin projects in Saudi Arabia for which the marine activities were ongoing during the 2010 quarter but were complete prior to the 2011 quarter.

[6] See Note 2 in the notes to the consolidated financial statements for a discussion of discontinued operations and other items.