Summary of Significant Accounting Policies (Details) (USD $)	Dec. 31, 2014 center	Dec. 31, 2013
Ownership Interests [Line Items]
Number of centers with ownership interest of less than 51%	10
Restricted Cash and Marketable Securities
Restricted cash and marketable securities, total	$ 30,300,000
Restricted cash and marketable securities, noncurrent	20,100,000
Restricted cash and marketable securities, current	10,219,000	0
Restricted marketable securities	$ 3,000,000
Consolidated [Member]
Ownership Interests [Line Items]
Number of centers with ownership interest of less than 51%	1
Nonconsolidated [Member]
Ownership Interests [Line Items]
Number of centers with ownership interest of less than 51%	9