Contingent Consideration - Maximum Amounts of Cash Obligations with Business Acquisitions and Strategic Investment (Details) $ in Millions	Sep. 30, 2015 USD ($)
Business Acquisition, Contingent Consideration [Line Items]
Total maximum cash obligations	$ 618.0
Liability recognized on financial statements	314.1
Business Acquisitions
Business Acquisition, Contingent Consideration [Line Items]
Total maximum cash obligations	390.0
NGP Investment
Business Acquisition, Contingent Consideration [Line Items]
Total maximum cash obligations	228.0
Contingent cash consideration | Performance-based
Business Acquisition, Contingent Consideration [Line Items]
Total maximum cash obligations	392.3
Liability recognized on financial statements	223.7
Contingent cash consideration | Employment-based
Business Acquisition, Contingent Consideration [Line Items]
Total maximum cash obligations	225.7
Liability recognized on financial statements	90.4
Contingent cash consideration | Business Acquisitions | Performance-based
Business Acquisition, Contingent Consideration [Line Items]
Total maximum cash obligations	209.3
Contingent cash consideration | Business Acquisitions | Employment-based
Business Acquisition, Contingent Consideration [Line Items]
Total maximum cash obligations	180.7
Contingent cash consideration | NGP Investment | Performance-based
Business Acquisition, Contingent Consideration [Line Items]
Total maximum cash obligations	183.0
Contingent cash consideration | NGP Investment | Employment-based
Business Acquisition, Contingent Consideration [Line Items]
Total maximum cash obligations	$ 45.0