Summary of Goodwill and Acquired Intangible Assets (Details 1) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Finite lived intangible assets
Gross carrying amount	$ 54,017	$ 29,117
Accumulated amortization	(28,796)	(27,540)
Membership rights [Member]
Finite lived intangible assets
Gross carrying amount	40,946	27,546
Accumulated amortization	(27,186)	(26,141)
Provider contracts [Member]
Finite lived intangible assets
Gross carrying amount	1,425	625
Accumulated amortization	(486)	(453)
Trademarks and other [Member]
Finite lived intangible assets
Gross carrying amount	11,646	946
Accumulated amortization	$ (1,124)	$ (946)