Business Segment and Geographic Information - Summary of Number of Customers Who Individually Make Up Greater than 10% of Total Revenues (Details) - Sales Revenue, Net - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
DaVita
Revenue, Major Customer [Line Items]
Percentage of revenues	20.00%	20.00%	20.00%
Fresenius
Revenue, Major Customer [Line Items]
Percentage of revenues	20.00%	18.00%	17.00%