Accounting Policies (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Variable interest entity
Cash and cash equivalents	$ 497,289	$ 515,164	$ 745,288	$ 673,092
Prepaid expenses and other	10,768	10,470
Deferred financing costs, net	47,484	50,214
Accrued liabilities	58,340	41,021
Other long-term liabilities	18,725	12,117
Kosmos Energy Finance International
Variable interest entity
Cash and cash equivalents	107,200	118,800
Prepaid expenses and other	300	200
Deferred financing costs, net	40,200	42,200
Accrued liabilities	300	500
Other long-term liabilities	$ 6,700	$ 6,600