Collaboration Agreements - Additional Information (Detail)	1 Months Ended		3 Months Ended		7 Months Ended	12 Months Ended	34 Months Ended
	Aug. 31, 2017 USD ($) employee $ / shares shares	Mar. 31, 2014 USD ($)	Mar. 31, 2018 USD ($) shares	Mar. 31, 2017 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated deferred revenue recognized within one year			$ 10,312,000					$ 9,229,000
Collaborative Arrangement | Celgene Corporation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and service revenue			(200,000)	$ 100,000
Deferred revenue recorded under collaboration agreement			5,900,000
Estimated deferred revenue recognized within one year			4,700,000
Maximum success-based milestone payments		$ 21,500,000
Collaborative Arrangement | Celgene Corporation | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum success-based milestone payments		27,300,000
Collaborative Arrangement | Celgene Corporation | Upfront Payment Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from collaborators						$ 6,000,000
Collaboration agreement upfront payment		$ 5,800,000					$ 2,100,000
Collaborative Arrangement | Merck Sharp & Dohme Corp.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from collaborators			600,000	1,800,000
Deferred revenue recorded under collaboration agreement			500,000
Collaborative Arrangement | Merck Sharp & Dohme Corp. | Upfront Payment Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and service revenue				8,500,000
Proceeds from collaborators				12,000,000	$ 3,900,000
Collaborative Arrangement | Lam Research Corporation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and service revenue			4,200,000
Maximum amount of royalties payable (ratio)	3
Maximum number of employees | employee	10
Exercise price of warrants | $ / shares	$ 16.75
Issued warrants, value	$ 6,700,000
Proceeds from collaborators			3,500,000
Deferred revenue recorded under collaboration agreement			1,400,000
Estimated deferred revenue recognized within one year			$ 600,000
Collaborative agreement period			1 year
Customer deposits			$ 6,200,000
Amounts due for services provided			0
Payments for services provided			$ 0
Number of warrants exercised | shares			0
Collaborative Arrangement | Lam Research Corporation | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and service revenue	$ 50,000,000
Number of warrants, outstanding | shares	1,000,000
Clinical Research Collaborative Arrangement | Merck Sharp & Dohme Corp.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and service revenue			$ 900,000	$ 2,100,000
Collaborative agreement period			1 year