Basis of Presentation (Details) $ in Thousands	Jun. 30, 2015 USD ($) center	Dec. 31, 2014 USD ($)
Ownership Interests [Line Items]
Number of ownership interests of less than 51% | center	13
Restricted Cash and Marketable Securities
Restricted cash and marketable securities, total	$ 30,200
Restricted cash and marketable securities, current	11,581	$ 10,219
Restricted cash and investments, noncurrent	18,600
Restricted marketable securities	$ 1,200
Consolidated [Member]
Ownership Interests [Line Items]
Number of ownership interests of less than 51% | center	2
Nonconsolidated [Member]
Ownership Interests [Line Items]
Number of ownership interests of less than 51% | center	11