Segment reporting - Summary of Assets by Segment (Phantom) (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Equity method and other investments	$ 226,309	$ 224,611
U.S. dialysis and related lab services
Segment Reporting Information [Line Items]
Equity method and other investments	101,173	95,290
Other—Ancillary services and strategic initiatives
Segment Reporting Information [Line Items]
Equity method and other investments	125,136	129,321
DMG held for sale
Segment Reporting Information [Line Items]
Equity method and other investments	$ 5,282	$ 4,833