Revenue - Composition of Total Revenue by Product and by U.S versus Rest of World (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Disaggregation Of Revenue [Line Items]
Total revenue	$ 164.0	$ 216.6	$ 545.4	$ 635.7
U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	153.0	204.4	510.0	601.9
RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	11.0	12.2	35.4	33.8
Molecular Diagnostic - Hereditary Cancer Testing [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	85.2	117.6	307.6	360.7
Molecular Diagnostic - Hereditary Cancer Testing [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	81.3	114.3	295.0	351.4
Molecular Diagnostic - Hereditary Cancer Testing [Member] | RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	3.9	3.3	12.6	9.3
Molecular Diagnostic - GeneSight [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	20.4	29.6	65.6	82.8
Molecular Diagnostic - GeneSight [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	20.4	29.6	65.6	82.8
Molecular Diagnostic - Prenatal [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	20.3	30.6	60.1	80.0
Molecular Diagnostic - Prenatal [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	20.2	30.6	59.9	80.0
Molecular Diagnostic - Prenatal [Member] | RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	0.1		0.2
Molecular Diagnostic - Vectra [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	10.5	11.3	31.8	36.1
Molecular Diagnostic - Vectra [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	10.5	11.3	31.8	36.1
Molecular Diagnostic - Prolaris [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	6.8	6.9	20.1	19.2
Molecular Diagnostic - Prolaris [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	6.8	6.9	20.0	19.1
Molecular Diagnostic - Prolaris [Member] | RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue			0.1	0.1
Molecular Diagnostic - EndoPredict [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	3.5	2.8	8.3	7.4
Molecular Diagnostic - EndoPredict [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	0.6	0.5	1.5	1.2
Molecular Diagnostic - EndoPredict [Member] | RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	2.9	2.3	6.8	6.2
Molecular Diagnostic - Other [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	3.8	1.7	10.1	6.3
Molecular Diagnostic - Other [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	3.6	1.5	9.9	5.8
Molecular Diagnostic - Other [Member] | RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	0.2	0.2	0.2	0.5
Molecular Diagnostic Testing [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	150.5	200.5	503.6	592.5
Molecular Diagnostic Testing [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	143.4	194.7	483.7	576.4
Molecular Diagnostic Testing [Member] | RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	7.1	5.8	19.9	16.1
Pharmaceutical and Clinical Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	13.5	16.1	41.8	43.2
Pharmaceutical and Clinical Services [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	9.6	9.7	26.3	25.5
Pharmaceutical and Clinical Services [Member] | RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	$ 3.9	$ 6.4	$ 15.5	$ 17.7