Accounting Policies (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Variable interest entity
Cash and cash equivalents	$ 508,874	$ 515,164	$ 629,951	$ 673,092
Prepaid expenses and other	14,409	10,470
Current derivative assets	1,254	1,061
Deferred financing costs, net	45,682	50,214
Accounts payable	63,955	128,855
Accrued liabilities	71,812	41,021
Other long-term liabilities	18,492	12,117
Kosmos Energy Finance International
Variable interest entity
Cash and cash equivalents	37,500	118,800
Prepaid expenses and other	500	200
Current derivative assets	1,300
Deferred financing costs, net	38,200	42,200
Accounts payable	300
Accrued liabilities	200	500
Other long-term liabilities	$ 7,600	$ 6,600