Summary of Significant Accounting Policies - Schedule of Cumulative Effect of Adopting ASU 2016-02 (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Mar. 31, 2019
Significant Accounting Policies [Line Items]
Operating lease right-of use assets	$ 22,798
Current portion of operating lease liability	3,157
Operating lease liability less current portion	21,139
Current portion of deferred lease rental benefit		$ 435
Deferred lease rental benefit, less current portion		1,144
Accumulated deficit	$ (458,708)	(381,025)
ASU 2016-02 [Member] \| Prior to Adoption of ASU 2016-02 [Member]
Significant Accounting Policies [Line Items]
Current portion of deferred lease rental benefit		435
Deferred lease rental benefit, less current portion		1,144
Accumulated deficit		(381,025)
ASU 2016-02 [Member] \| Effect of Adoption of ASU 2016-02 [Member]
Significant Accounting Policies [Line Items]
Operating lease right-of use assets		18,478
Current portion of operating lease liability		3,130
Operating lease liability less current portion		16,564
Current portion of deferred lease rental benefit		(435)
Deferred lease rental benefit, less current portion		(1,144)
Accumulated deficit		363
ASU 2016-02 [Member] \| After the Adoption of ASU 2016-02 [Member]
Significant Accounting Policies [Line Items]
Operating lease right-of use assets		18,478
Current portion of operating lease liability		3,130
Operating lease liability less current portion		16,564
Accumulated deficit		$ (380,662)

Significant accounting policies.

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- Definition

For a classified balance sheet, the cumulative difference as of the balance sheet date between the payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense, by the lessor or lessee, respectively, within one year of the balance sheet date.

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For a classified balance sheet, the cumulative difference between the rental income or payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense, by the lessor or lessee, respectively, more than one year after the balance sheet date.

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Present value of lessee's discounted obligation for lease payments from operating lease, classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

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Present value of lessee's discounted obligation for lease payments from operating lease, classified as noncurrent.

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Amount of lessee's right to use underlying asset under operating lease.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(30)(a)(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(23)(a)(4))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
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-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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