Claims Payable (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Components of the change in claims payable
Medical claims payable, beginning of the year	$ 510,675	$ 529,036	$ 536,107
Health benefits expense incurred during the year:
Related to current year	5,365,247	4,828,321	4,492,590
Related to prior years	(92,988)	(106,215)	(85,317)
Total incurred	5,272,259	4,722,106	4,407,273
Health benefits payments during the year:
Related to current year	4,823,667	4,359,216	4,007,789
Related to prior years	385,819	381,251	406,555
Total payments	5,209,486	4,740,467	4,414,344
Medical claims payable, end of the year	$ 573,448	$ 510,675	$ 529,036
Current year medical claims paid as a percent of current year health benefits expense incurred	89.90%	90.30%	89.20%
Health benefits expense incurred related to prior years as a percent of prior year medical claims payable as of December 31	(18.20%)	(20.10%)	(15.90%)
Health benefits expense incurred related to prior years as a percent of the prior year's health benefits expense related to current year	(1.90%)	(2.40%)	(2.30%)