Commitments and Contingencies - Additional Information (Detail)		1 Months Ended							12 Months Ended
	May 31, 2015 USD ($)	Jul. 31, 2017 USD ($)	Apr. 30, 2017 ft²	Feb. 28, 2017 USD ($)	Dec. 31, 2016 USD ($) ft²	Mar. 31, 2015 USD ($) ft²	Nov. 30, 2014 USD ($) shares	Aug. 31, 2014	Dec. 31, 2018 USD ($) Patent	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) ft²	Dec. 09, 2016 Patent
Other Commitments [Line Items]
Lease expense, payment due									$ 3,989,000
Rent expense									$ 4,000,000	$ 2,500,000	$ 2,400,000
Standard product warranty, description									Limited one- to five-year warranty
Retainer fees									$ 48,459,000	37,560,000	33,729,000
Contingent liabilities									$ 0	0
Boston Scientific Corporation [Member]
Other Commitments [Line Items]
Patent infringement lawsuit allegation against number of patents | Patent									8			10
Indemnification Agreement [Member]
Other Commitments [Line Items]
Contingent liabilities									$ 0
Patent Infringement [Member]
Other Commitments [Line Items]
Contingent liabilities									0
Service Agreement [Member]
Other Commitments [Line Items]
Service agreement commitment amount									2,400,000
Licensing Agreements [Member]
Other Commitments [Line Items]
Annual royalty payment									$ 3,100,000	$ 2,500,000	$ 1,900,000
License agreement commitment amount		$ 400,000
License agreement expiration year		2022
Licensing Agreements [Member] | Mayo And VGL [Member]
Other Commitments [Line Items]
License agreement, terms									The agreement will terminate upon the last to expire patent application, unless terminated earlier. The agreement can be terminated any time after three years from March 2006 by Mayo or VGL.
Licensing Agreements [Member] | Mayo Foundation [Member]
Other Commitments [Line Items]
Retainer fees									$ 40,000
Common stock, shares issued | shares							20,833
Noncash research and development expense							$ 500,000
Licensing Agreements [Member] | Mayo Foundation [Member] | Minimum [Member]
Other Commitments [Line Items]
Annual royalty payment									200,000
Supply Agreements [Member]
Other Commitments [Line Items]
Purchase commitment, amount due in 2019									6,200,000
Purchase commitment, amount due in 2020									$ 6,000,000
Redwood Office Agreement [Member]
Other Commitments [Line Items]
Lease agreement, commencement period									2015-03
Area of office space | ft²						50,740
Lease agreement, effective date						Jun. 30, 2015
Lease agreement, expiration period						2022-05
Lease expense, payment due						$ 2,000,000
Annual lease expense payable in final year of lease term						$ 2,400,000
Redwood Office Agreement Additional Expansion Premises [Member]
Other Commitments [Line Items]
Area of office space | ft²			8,171
Redwood Office Agreement Additional Expansion Premises [Member] | Amendment 1 [Member]
Other Commitments [Line Items]
Area of office space | ft²					49,980						49,980
Lease expense, payment due					$ 1,200,000						$ 1,200,000
Annual lease expense payable in final year of lease term					$ 2,900,000						$ 2,900,000
Commencement date description									The lease for the Expansion Premises commenced on June 1, 2018.
Lease commencement date					Jun. 01, 2018
Lease agreement, expiration date					May 31, 2025
Redwood Office Agreement Additional Expansion Premises [Member] | Amendment 2 [Member]
Other Commitments [Line Items]
Lease agreement, effective date			May 31, 2017
Lease agreement, expiration date			Jun. 01, 2018
Facility Lease Agreement, Original [Member]
Other Commitments [Line Items]
Lease agreement, commencement period								2014-08
Lease agreement, effective date								Aug. 21, 2014
Lease agreement, expiration date								May 31, 2015
Lease agreement, lease expense	$ 100,000
Facility Lease Agreement, Extended [Member]
Other Commitments [Line Items]
Lease agreement, commencement period						2015-03
Lease agreement, expiration period						2017-02
Lease agreement, lease expense				$ 300,000
Non-cancellable Facility Lease [Member]
Other Commitments [Line Items]
Lease agreement, effective date				Mar. 01, 2017
Lease agreement, expiration date				Feb. 28, 2022
Lease agreement, lease expense				$ 400,000