Summary of Significant Accounting Policies - Concentration Risk (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Concentration of Business
Net revenue	$ 1,268,743	$ 1,190,082	$ 1,157,607	$ 980,968	$ 982,459	$ 923,170	$ 888,014	$ 966,475	$ 4,597,400	$ 3,760,118	$ 3,546,317
Minimum
Concentration of Business
Term of Contract									1 year
Term of renewed contract									1 year
Notice period for termination of contract									60 days
Maximum
Concentration of Business
Term of Contract									3 years
Term of renewed contract									2 years
Notice period for termination of contract									180 days
Pennsylvania Counties
Concentration of Business
Net revenue									$ 395,700	$ 369,900	$ 359,000