Segment reporting - Summary of Segment Net Revenues, Segment Operating Income (Loss) and Reconciliation of Segment Income to Consolidated Income Before Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	$ 2,635,152	$ 2,591,074
Provision for uncollectible accounts	(5,463)	25,545
Net U.S. dialysis and related lab services patient service revenues	2,629,689	2,616,619
Other revenues	113,423	232,825
Total revenues	2,743,112	2,849,444
Operating income (loss)	340,507	410,686
Corporate administrative support	(18,844)	(15,704)
Debt expense	(131,519)	(113,516)
Other income, net	6,940	4,582
Income from continuing operations before income taxes	215,928	301,752
U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
Total revenues	2,516,510	2,519,478
Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Total revenues	226,602	329,966
Operating Segments
Segment Reporting Information [Line Items]
Total revenues	2,777,089	2,878,065
Operating income (loss)	359,351	426,390
Operating Segments | U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	2,547,709	2,507,587
Provision for uncollectible accounts	(5,463)	25,199
Net U.S. dialysis and related lab services patient service revenues	2,542,246	2,532,786
Total revenues	2,547,151	2,537,900
Operating income (loss)	416,981	433,380
Operating Segments | U.S. dialysis and related lab services | External Sources
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	2,517,289	2,489,165
Other revenues	4,684	5,114
Operating Segments | U.S. dialysis and related lab services | Intersubsegment Eliminations
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	30,420	18,422
Other revenues	221	0
Operating Segments | Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	117,863	102,255
Other revenues	108,739	227,711
Total revenues	229,938	340,165
Operating income (loss)	(57,630)	(6,990)
Operating Segments | Other—Ancillary services and strategic initiatives | Intersubsegment Eliminations
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	3,336	10,199
Intersegment Elimination
Segment Reporting Information [Line Items]
Total revenues	(33,977)	(28,621)
Intersegment Elimination | U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
Total revenues	(30,641)	(18,422)
Intersegment Elimination | Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Total revenues	$ (3,336)	$ (10,199)