Related Party Transactions - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Recognized revenue	$ 43,477,000	$ 13,444,000	$ 858,000
Cost of related-party revenue	3,770,000	2,736,000
Accounts receivable	2,007,000	403,000
Roche related-party deferred revenue	3,747,000	$ 3,742,000
Roche [Member]
Related Party Transaction [Line Items]
Recognized revenue	$ 43,477,000		$ 858,000
Related party revenue to net revenue, percentage	37.00%	14.40%	1.40%
Cost of related-party revenue	$ 3,770,000
Accounts receivable	2,007,000	$ 403,000
Roche related-party deferred revenue	3,747,000	3,742,000
Amount of related party transaction during the period	0	0	$ 0
Roche [Member] \| Molecular Information Platform Program [Member]
Related Party Transaction [Line Items]
Recognized revenue	19,476,000	13,444,000
Cost of related-party revenue		2,736,000
Roche [Member] \| Circulating Tumor DNA Platform Program [Member]
Related Party Transaction [Line Items]
Clinical milestone payments recognized	12,000,000
Roche [Member] \| CDx Development, Immunotherapy Testing Platform Development, and Other R&D Programs [Member]
Related Party Transaction [Line Items]
Recognized revenue	9,984,000
Roche [Member] \| Other Collaboration Agreement [Member]
Related Party Transaction [Line Items]
Recognized revenue	2,017,000
Board of Directors [Member]
Related Party Transaction [Line Items]
Recognized revenue	1,631,000	1,716,000	$ 641,000
Accounts receivable	$ 0	$ 825,000

Deferred revenue related party.

No definition available.

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- Definition

Percentage of related party revenue to net revenue of the reporting entity during the period.

+ References

No definition available.

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- Definition

Amount of receivables arising from transactions with related parties due within one year or the normal operating cycle, if longer.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Costs of sales and operating expenses for the period incurred from transactions with related parties.

+ References

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- Definition

Amount of transactions with related party during the financial reporting period.

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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.

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- Definition

The amount of consideration recognized during the period for the milestone or milestones.

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