Noncontrolling interests subject to put provisions and other commitments - additional information (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Minimum
Other Commitments [Line Items]
Scheduled dissolution term of joint ventures	10 years
Maximum
Other Commitments [Line Items]
Scheduled dissolution term of joint ventures	50 years
Commitments to provide operating capital
Other Commitments [Line Items]
Other potential commitments to provide operating capital to several dialysis centers	$ 5,264