Revenue - Composition of Total Revenue by Product and U.S versus Rest of World (Detail) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Disaggregation Of Revenue [Line Items]
Total revenue	$ 186.3	$ 202.3
U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	174.7	191.6
RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	11.7	10.7
Molecular Diagnostic - Hereditary Cancer Testing [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	104.5	116.3
Molecular Diagnostic - Hereditary Cancer Testing [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	100.6	113.5
Molecular Diagnostic - Hereditary Cancer Testing [Member] | RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	3.9	2.8
Molecular Diagnostic - GeneSight [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	22.7	29.3
Molecular Diagnostic - GeneSight [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	22.7	29.3
Molecular Diagnostic - Prenatal [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	23.5	18.1
Molecular Diagnostic - Prenatal [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	23.5	18.1
Molecular Diagnostic- VectraDA [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	11.0	13.0
Molecular Diagnostic- VectraDA [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	11.0	13.0
Molecular Diagnostic - Prolaris [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	6.5	6.2
Molecular Diagnostic - Prolaris [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	6.5	6.2
Molecular Diagnostic - EndoPredict [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	2.3	2.4
Molecular Diagnostic - EndoPredict [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	0.5	0.3
Molecular Diagnostic - EndoPredict [Member] | RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	1.8	2.1
Molecular Diagnostic - Other [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	1.5	3.7
Molecular Diagnostic - Other [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	1.4	3.6
Molecular Diagnostic - Other [Member] | RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	0.1	0.1
Molecular Diagnostic Testing [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	172.0	189.0
Molecular Diagnostic Testing [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	166.2	184.0
Molecular Diagnostic Testing [Member] | RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	5.8	5.0
Pharmaceutical and Clinical Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	14.3	13.3
Pharmaceutical and Clinical Services [Member] | U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	8.5	7.6
Pharmaceutical and Clinical Services [Member] | RoW [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	$ 5.9	$ 5.7