Net Loss Per Share - Computation of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net loss attributable to CareDx, Inc. used to compute basic and diluted net loss per share	$ (8,969)	$ (5,562)
Denominator:
Weighted-average shares used to compute basic and diluted net loss per share attributable to CareDx, Inc.	29,615,441	21,343,782
Net loss per share attributable to CareDx, Inc.:
Basic and diluted	$ (0.30)	$ (0.26)