Net Loss Per Share - Computation of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net loss attributable to CareDx, Inc. used to compute basic net loss per share	$ (14,268)	$ (3,764)	$ (23,798)	$ (23,989)
Less: Gain on private placement warrants	0	(1,386)	0	0
Net loss attributable to CareDx, Inc. used to compute diluted net loss per share	$ (14,268)	$ (5,150)	$ (23,798)	$ (23,989)
Denominator:
Weighted-average shares used to compute basic net loss per share attributable to CareDx, Inc.	22,526,615	19,098,626	21,765,292	14,894,218
Add: Private placement warrant shares	0	382,798	0	0
Weighted-average shares used to compute diluted net loss per share attributable to CareDx, Inc.	22,526,615	19,481,424	21,765,292	14,894,218
Net loss per share attributable to CareDx, Inc.:
Basic	$ (0.63)	$ (0.20)	$ (1.09)	$ (1.61)
Diluted	$ (0.63)	$ (0.26)	$ (1.09)	$ (1.61)