Acquisitions and divestitures - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) clinic	Mar. 31, 2018 USD ($)
Business Acquisition [Line Items]
Cash paid to acquire businesses	$ 11,274	$ 16,582
Contingent earn-out obligations and liabilities assumed associated with acquisitions	11,716
Other Accrued Liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations	650
Other long-term liabilities
Business Acquisition [Line Items]
Contingent earn-out obligations	2,782
Other companies
Business Acquisition [Line Items]
Contingent earn-out obligations	$ 3,432
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	$ 10,210
Deferred purchase price obligations	1,457
Contingent earn-out obligations and liabilities assumed associated with acquisitions	898
Goodwill deductible for tax purposes associated with acquisitions	$ 6,945
Noncompete Agreements
Business Acquisition [Line Items]
Amortizable intangible assets acquired, weighted-average estimated useful lives	5 years
U.S. dialysis and related lab services | Dialysis and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | clinic	2
Foreign Dialysis Centers | Dialysis and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | clinic	2