Summary of Significant Accounting Policies (Details) $ in Millions	Dec. 31, 2015 USD ($) center	Dec. 31, 2014 USD ($)
Ownership Interests [Line Items]
Number of centers with ownership interest of less than 51% | center	23
Restricted Cash and Marketable Securities
Restricted cash and marketable securities, total	$ 27.4	$ 30.3
Restricted cash and marketable securities, noncurrent	13.9	20.1
Restricted marketable securities	$ 2.7	3.0
Consolidated [Member]
Ownership Interests [Line Items]
Number of centers with ownership interest of less than 51% | center	2
Nonconsolidated [Member]
Ownership Interests [Line Items]
Number of centers with ownership interest of less than 51% | center	21
New Accounting Pronouncement, Early Adoption, Effect [Member]
Ownership Interests [Line Items]
Deferred tax assets, net, current		$ 22.5