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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	$ 2,670,701	$ 2,561,543	$ 7,980,178	$ 7,478,938
Provision for uncollectible accounts	(11,977)	(119,321)	(35,838)	(335,979)
Net U.S. dialysis and related lab services patient service revenues	2,658,724	2,442,222	7,944,340	7,142,959
Other revenues	188,606	322,849	639,387	952,762
Total revenues	2,847,330	2,765,071	8,583,727	8,095,721
Operating income (loss)	289,038	395,294	1,137,916	1,662,418
Corporate administrative support	(40,836)	(10,965)	(70,605)	(32,587)
Debt expense	(125,927)	(109,306)	(359,135)	(321,637)
Other income, net	4,007	3,396	10,583	12,180
Income from continuing operations before income taxes	167,118	289,384	789,364	1,352,961
U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
Total revenues	2,551,377	2,356,999	7,639,101	6,928,323
Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Total revenues	295,953	408,072	944,626	1,167,398
Operating Segments
Segment Reporting Information [Line Items]
Total revenues	2,881,115	2,784,542	8,675,418	8,152,768
Operating income (loss)	329,874	406,259	1,208,521	1,695,005
Operating Segments | U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	2,584,769	2,483,644	7,725,187	7,285,962
Provision for uncollectible accounts	(12,900)	(117,962)	(37,108)	(334,031)
Net U.S. dialysis and related lab services patient service revenues	2,571,869	2,365,682	7,688,079	6,951,931
Other revenues	4,932	4,792	14,965	14,951
Total revenues	2,576,801	2,370,474	7,703,044	6,966,882
Operating income (loss)	390,006	442,777	1,272,828	1,837,989
Operating Segments | U.S. dialysis and related lab services | External Sources
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	2,559,345	2,470,169	7,661,244	7,247,403
Operating Segments | U.S. dialysis and related lab services | Intersubsegment Eliminations
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	25,424	13,475	63,943	38,559
Operating Segments | Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	112,279	90,015	320,204	229,587
Other revenues	183,674	318,057	624,422	937,811
Total revenues	304,314	414,068	972,374	1,185,886
Operating income (loss)	(60,132)	(36,518)	(64,307)	(142,984)
Operating Segments | Other—Ancillary services and strategic initiatives | Intersubsegment Eliminations
Segment Reporting Information [Line Items]
Dialysis and related lab patient service revenues	8,361	5,996	27,748	18,488
Intersegment Elimination
Segment Reporting Information [Line Items]
Total revenues	(33,785)	(19,471)	(91,691)	(57,047)
Intersegment Elimination | U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
Total revenues	(25,424)	(13,475)	(63,943)	(38,559)
Intersegment Elimination | Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Total revenues	$ (8,361)	$ (5,996)	$ (27,748)	$ (18,488)