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, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
U.S. dialysis and related lab services patient service revenues	$ 2,713,281	$ 2,629,689
Other revenues	127,956	113,423
Total revenues	2,841,237	2,743,112
Operating income (loss)	465,376	340,507
Corporate administrative support	(23,585)	(18,844)
Debt expense	(88,603)	(131,519)
Debt refinancing charges	(2,948)	0
Other (loss) income, net	(4,350)	6,940
Income from continuing operations before income taxes	369,475	215,928
U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
Total revenues	2,584,381	2,516,510
Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Total revenues	256,856	226,602
Operating Segments
Segment Reporting Information [Line Items]
Total revenues	2,877,631	2,777,089
Operating income (loss)	488,961	359,351
Operating Segments | U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
U.S. dialysis and related lab services patient service revenues	2,611,181	2,542,246
Total revenues	2,616,623	2,547,151
Operating income (loss)	491,607	416,981
Operating Segments | U.S. dialysis and related lab services | External Sources
Segment Reporting Information [Line Items]
Dialysis patient service revenues	2,579,240	2,511,826
Other revenues	5,141	4,684
Operating Segments | U.S. dialysis and related lab services | Intersubsegment Eliminations
Segment Reporting Information [Line Items]
Dialysis patient service revenues	31,941	30,420
Other revenues	301	221
Operating Segments | Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Dialysis patient service revenues	134,041	117,863
Other revenues	122,815	108,739
Total revenues	261,008	229,938
Operating income (loss)	(2,646)	(57,630)
Operating Segments | Other—Ancillary services and strategic initiatives | Intersubsegment Eliminations
Segment Reporting Information [Line Items]
Dialysis patient service revenues	4,152	3,336
Intersegment Elimination
Segment Reporting Information [Line Items]
Total revenues	(36,394)	(33,977)
Intersegment Elimination | U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
Total revenues	(32,242)	(30,641)
Intersegment Elimination | Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Total revenues	$ (4,152)	$ (3,336)