Acquisitions and divestitures - Additional Information (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) clinic	Jun. 30, 2018 USD ($)
Business Acquisition [Line Items]
Cash paid to acquire businesses	$ 65,970	$ 89,465
Deferred purchase price obligations	12,484
Contingent earn-out obligations and liabilities assumed associated with acquisitions	25,875
Other Accrued Liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations	4,090
Other long-term liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations	10,640
Other companies
Business Acquisition [Line Items]
Contingent earn-out obligations	$ 14,730
Minimum | Other companies | EBITDA or Operating Income Performance Targets or Quality Margins
Business Acquisition [Line Items]
Earn-out consideration payment period	1 year
Maximum | Other companies | EBITDA or Operating Income Performance Targets or Quality Margins
Business Acquisition [Line Items]
Earn-out consideration payment period	5 years
Dialysis and other businesses
Business Acquisition [Line Items]
Cash paid to acquire businesses	$ 63,945
Deferred purchase price obligations	453
Goodwill deductible for tax purposes associated with acquisitions	$ 64,905
Noncompete Agreements
Business Acquisition [Line Items]
Amortizable intangible assets acquired, weighted-average estimated useful lives	6 years
U.S. dialysis and related lab services | Dialysis and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | clinic	5
Foreign Dialysis Centers | Dialysis and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | clinic	7