Commitments and Contingencies - Additional Information (Details)		3 Months Ended
Oct. 04, 2018 USD ($) ft²	Mar. 31, 2019 USD ($)
Lessee Lease Description [Line Items]
Operating lease, cost		$ 1,300,000
Cash paid for operating leases		$ 1,400,000
Operating leases, weighted average remaining lease term		3 years 11 months 12 days
Operating leases, weighted-average discount rate		4.75%
Office Lease \| San Francisco
Lessee Lease Description [Line Items]
Lease rentable area \| ft²	117,560
Lease expected commencement period	second quarter of 2019
Lease term	12 years
Lease expiration date	Aug. 31, 2031
Renewal term of lease	5 years
Annual rental payments	$ 10,000,000
Percentage of increase to rental payments, each year	3.00%
Office Lease \| San Francisco \| Standby Letters of Credit
Lessee Lease Description [Line Items]
Proceeds from line of credit	$ 6,900,000
Office Lease \| San Francisco \| Maximum
Lessee Lease Description [Line Items]
Tenant improvement allowance	$ 2,400,000

Lease expected commencement period.

No definition available.

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- Definition

Operating lease rentable area.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Percentage of increase to rental payment, annual.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Date which lease or group of leases is set to expire, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

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- Definition

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.

+ References

No definition available.

+ Details

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- Definition

Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

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Period Type:	instant

- Definition

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

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Period Type:	instant

- Definition

Amount of single lease cost, calculated by allocation of remaining cost of lease over remaining lease term. Includes, but is not limited to, single lease cost, after impairment of right-of-use asset, calculated by amortization of remaining right-of-use asset and accretion of lease liability.

+ References

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Balance Type:	debit
Period Type:	duration

- Definition

Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Weighted average discount rate for operating lease calculated at point in time.

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Period Type:	instant

- Definition

Weighted average remaining lease term for operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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- Definition

This element represents the payments that the lessee is obligated to make or can be required to make in connection with a property under the terms of an agreement classified as an operating lease, excluding contingent rentals and a guarantee by the lessee of the lessor's debt and the lessee's obligation to pay (apart from the rental payments) executory costs such as insurance, maintenance, and taxes.

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- Definition

The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

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- Definition

Carrying amount as of the balance sheet date of improvements having a life longer than one year that were made for the benefit of one or more tenants.

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