Claims Payable (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Components of the change in claims payable
Claims payable, beginning of period	$ 573,448	$ 510,675
Health benefits expense incurred during the period:
Related to current year	5,661,449	3,965,890
Related to prior years	(99,287)	(84,520)
Total incurred	5,562,162	3,881,370
Health benefits payments during the period:
Related to current year	4,921,383	3,461,910
Related to prior years	443,810	385,609
Total payments	5,365,193	3,847,519
Claims payable, end of period	$ 770,417	$ 544,526