Organization (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	1 Months Ended		12 Months Ended
	May 16, 2011 vote	Jun. 30, 2011	Jun. 30, 2011	Dec. 31, 2011	Dec. 31, 2012 item
Organization
Number of common shares into which the units were exchanged	341,200,000
Voting rights per common share	1
Common shares, par value (in dollars per share)	$ 0.01			$ 0.01	$ 0.01
Number of classes of common stock					1
Common shares issued under IPO	33,000,000
Shares issued pursuant to over-allotment option		1,500,000
Total number of common shares sold under the IPO			34,500,000
Net proceeds from the initial public offering			$ 580,400	$ 580,374
Service Vesting Restricted Stock Awards
Organization
Unvested profit units exchanged for service vesting restricted stock awards (in shares)	10,000,000
Kosmos Energy Holdings | Convertible preferred units
Organization
Number of common shares into which the units were exchanged	277,700,000
Kosmos Energy Holdings | Common units
Organization
Number of common shares into which the units were exchanged	63,500,000