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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	$ 2,734,065	$ 2,718,403	$ 5,369,217	$ 5,309,477
Provision for uncollectible accounts	(10,249)	(49,406)	(15,712)	(23,861)
Net U.S. dialysis and related lab services patient service revenues	2,723,816	2,668,997	5,353,505	5,285,616
Other revenues	118,889	217,956	232,312	450,781
Total revenues	2,842,705	2,886,953	5,585,817	5,736,397
Operating income (loss)	461,886	438,192	802,393	848,878
Corporate administrative support	(22,021)	(14,066)	(40,866)	(29,769)
Debt expense	(131,666)	(119,692)	(263,185)	(233,208)
Debt prepayment charges	(12,160)	0	(12,160)	0
Other income, net	5,643	1,994	12,583	6,576
Income from continuing operations before income taxes	323,703	320,494	539,631	622,246
U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
Total revenues	2,607,160	2,568,247	5,123,670	5,087,724
Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Total revenues	235,545	318,706	462,147	648,673
Operating Segments
Segment Reporting Information [Line Items]
Total revenues	2,876,442	2,916,238	5,653,531	5,794,303
Operating income (loss)	483,907	452,258	843,259	878,647
Operating Segments | U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	2,642,242	2,632,830	5,189,951	5,140,418
Provision for uncollectible accounts	(10,249)	(49,406)	(15,712)	(24,208)
Net U.S. dialysis and related lab services patient service revenues	2,631,993	2,583,424	5,174,239	5,116,210
Total revenues	2,637,494	2,588,343	5,184,645	5,126,243
Operating income (loss)	498,957	449,443	915,939	882,822
Operating Segments | U.S. dialysis and related lab services | External Sources
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	2,612,200	2,612,734	5,129,489	5,101,899
Other revenues	5,209	4,919	9,893	10,033
Operating Segments | U.S. dialysis and related lab services | Intersubsegment Eliminations
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	30,042	20,096	60,462	38,519
Other revenues	292	0	513	0
Operating Segments | Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	121,865	105,669	239,728	207,925
Other revenues	113,680	213,037	222,419	440,748
Total revenues	238,948	327,895	468,886	668,060
Operating income (loss)	(15,050)	2,815	(72,680)	(4,175)
Operating Segments | Other—Ancillary services and strategic initiatives | Intersubsegment Eliminations
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	3,403	9,189	6,739	19,387
Intersegment Elimination
Segment Reporting Information [Line Items]
Total revenues	(33,737)	(29,285)	(67,714)	(57,906)
Intersegment Elimination | U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
Total revenues	(30,334)	(20,096)	(60,975)	(38,519)
Intersegment Elimination | Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Total revenues	$ (3,403)	$ (9,189)	$ (6,739)	$ (19,387)