Segment reporting - Summary of Expenditures for Property and Equipment by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Expenditures for property and equipment	$ 231,682	$ 240,889	$ 705,659	$ 639,829
U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
Expenditures for property and equipment	214,728	207,472	603,186	538,620
Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Expenditures for property and equipment	5,019	9,135	37,191	28,256
DMG held for sale
Segment Reporting Information [Line Items]
Expenditures for property and equipment	$ 11,935	$ 24,282	$ 65,282	$ 72,953