Summary of Significant Accounting Policies - Summary of Revenue from Contracts with Customers by Payor Type (Detail) - Accounting Standards Update 2014-09 - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2018
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers by payor type	$ 5,625	$ 15,678
Genetic Testing Services \| Institutional
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers by payor type	5,334	14,594
Genetic Testing Services \| Patient
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers by payor type	148	407
Genetic Testing Services \| Insurance
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers by payor type	$ 143	$ 677

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration