Revenue - Revenue Disaggregated by Type of Service (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Molecular Information Services [Member]
Disaggregation Of Revenue [Line Items]
Revenue	$ 31,943	$ 15,594
Pharma Research and Development Services [Member]
Disaggregation Of Revenue [Line Items]
Revenue	4,782	1,087
Third Party [Member]
Disaggregation Of Revenue [Line Items]
Revenue	36,725	16,681
Third Party [Member] \| Molecular Information Services [Member]
Disaggregation Of Revenue [Line Items]
Revenue	31,943	15,594
Third Party [Member] \| Molecular Information Services [Member] \| Clinical Sample Profiling Services [Member]
Disaggregation Of Revenue [Line Items]
Revenue	15,589	10,649
Third Party [Member] \| Molecular Information Services [Member] \| Pharma Sample Profiling Services [Member]
Disaggregation Of Revenue [Line Items]
Revenue	13,106	2,454
Third Party [Member] \| Molecular Information Services [Member] \| Other Molecular Information Services [Member]
Disaggregation Of Revenue [Line Items]
Revenue	3,248	2,491
Third Party [Member] \| Pharma Research and Development Services [Member]
Disaggregation Of Revenue [Line Items]
Revenue	4,782	1,087
Third Party [Member] \| Pharma Research and Development Services [Member] \| R&D and Regulatory Services [Member]
Disaggregation Of Revenue [Line Items]
Revenue	4,782	1,087
Roche [Member]
Disaggregation Of Revenue [Line Items]
Related-party revenue	16,115	9,647
Roche [Member] \| Molecular Information Services [Member]
Disaggregation Of Revenue [Line Items]
Related-party revenue	14,648	5,504
Roche [Member] \| Molecular Information Services [Member] \| Clinical Sample Profiling Services [Member]
Disaggregation Of Revenue [Line Items]
Related-party revenue	3,198	970
Roche [Member] \| Molecular Information Services [Member] \| Pharma Sample Profiling Services [Member]
Disaggregation Of Revenue [Line Items]
Related-party revenue	10,450	3,534
Roche [Member] \| Molecular Information Services [Member] \| Other Molecular Information Services [Member]
Disaggregation Of Revenue [Line Items]
Related-party revenue	1,000	1,000
Roche [Member] \| Pharma Research and Development Services [Member]
Disaggregation Of Revenue [Line Items]
Related-party revenue	1,467	4,143
Roche [Member] \| Pharma Research and Development Services [Member] \| R&D and Regulatory Services [Member]
Disaggregation Of Revenue [Line Items]
Related-party revenue	$ 1,467	$ 4,143

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07.1(c))
-URI http://asc.fasb.org/extlink&oid=6488393&loc=d3e606610-122999

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- Definition

Amount before allowances and discounts of service revenue classified as other.

+ References

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