Segment Reporting - Operating Results of Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net revenues	$ 10,735	$ 7,129	$ 17,297	$ 14,344
Operating loss	(6,968)	(2,886)	(13,538)	(4,277)
Depreciation and amortization	843	193	1,104	358
Total assets	100,453		100,453		$ 55,638
CareDx [Member]
Segment Reporting Information [Line Items]
Net revenues	7,260	7,129	13,822	14,344
Operating loss	(5,243)	(2,886)	(11,813)	(4,277)
Depreciation and amortization	299	193	560	358
Total assets	42,707		42,707		55,638
Allenex [Member]
Segment Reporting Information [Line Items]
Net revenues	3,475	0	3,475	0
Operating loss	(1,725)	0	(1,725)	0
Depreciation and amortization	544	$ 0	544	$ 0
Total assets	$ 57,746		$ 57,746		$ 0