Stock-based compensation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Deferred Compensation Arrangement with Individual, Share-based Payments
Allocated Share-based Compensation Expense	$ 5.2	$ 4.1	$ 9.2	$ 7.3
2010 Employee Stock Purchase Plan (ESPP)
Deferred Compensation Arrangement with Individual, Share-based Payments
Employee stock purchase plan shares issued during period			125,101
Selling, General and Administrative Expenses [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments
Allocated Share-based Compensation Expense	$ 5.2	3.9	$ 9.2	7.0
Physician Segment [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments
Allocated Share-based Compensation Expense		$ 0.2		$ 0.3