Acquisitions and divestitures - Additional Information (Detail) $ in Thousands	1 Months Ended	3 Months Ended
	Dec. 31, 2012 Entity	Mar. 31, 2017 USD ($) Clinic	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Cash paid to acquire businesses		$ 77,236	$ 405,154
Contingent earn-out obligations associated with acquisitions		$ 13,754
Amortizable intangible assets acquired, weighted-average estimated useful lives		5 years
Business Combination, Contingent Consideration, Liability		$ 8,565		$ 9,977
Other Accrued Liabilities
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability		4,653
Other long-term liabilities
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability		3,912
Other companies
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability		$ 8,565
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		7 years
Dialysis businesses and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | Entity	2
Cash paid to acquire businesses		$ 77,236
Deferred purchase price obligations		2,205
Contingent earn-out obligations associated with acquisitions		1,495
Goodwill deductible for tax purposes associated with acquisitions		$ 69,691
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 businesses and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | Clinic		12
Foreign Dialysis Centers | Dialysis businesses and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | Clinic		3
Other Medical Businesses | Dialysis businesses and other businesses
Business Acquisition [Line Items]
Number of businesses acquired | Clinic		2