Significant Accounting Policies (Goodwill and Other Intangible Assets) (Details) (USD $)			6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Provider Networks [Member]	Dec. 31, 2012 Provider Networks [Member]	Jun. 30, 2013 Customer Relationships and Other [Member]	Dec. 31, 2012 Customer Relationships and Other [Member]	Jun. 30, 2013 Western Region Operations [Member]	Dec. 31, 2012 Western Region Operations [Member]	Jun. 30, 2012 Western Region Operations [Member]
Goodwill [Line Items]
Goodwill	$ 565,886,000	$ 565,886,000					$ 565,900,000	$ 565,900,000
Ratio of fair value to carrying value							149.00%		115.00%
Finite-Lived Intangible Assets
Gross Carrying Amount	70,000,000	70,000,000	40,500,000	40,500,000	29,500,000	29,500,000
Accumulated Amortization	(54,400,000)	(52,700,000)	(35,100,000)	(34,600,000)	(19,300,000)	(18,100,000)
Net Balance	15,600,000	17,300,000	5,400,000	5,900,000	10,200,000	11,400,000
Weighted Average Life (in years)			19 years 4 months 24 days	19 years 4 months 24 days	11 years 1 month 6 days	11 years 1 month 6 days
Future Amortization Expense, Current to Five Succeeding Fiscal Years
2013	3,400,000
2014	2,800,000
2015	2,600,000
2016	2,000,000
2017	$ 2,000,000