Commitments and Contingencies - Narrative (Details)		1 Months Ended		12 Months Ended				24 Months Ended
	Jun. 30, 2017 USD ($)	Apr. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 USD ($) ft² multiplier	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2012 USD ($)	Mar. 01, 2019	Feb. 28, 2019 USD ($)
Long-term Purchase Commitment [Line Items]
Lease area space occupancy | ft²				107,200
Payments for capital improvements		$ 300,000	$ 400,000
Rent expense				$ 3,200,000	$ 3,200,000	$ 2,900,000
Sublease rentals				1,100,000	1,400,000	$ 1,200,000
Term of contract		3 years	3 years			3 years
Indemnification agreement
Long-term Purchase Commitment [Line Items]
Accruals for expenses related to indemnification issues				$ 0
Term Debt
Long-term Purchase Commitment [Line Items]
Current borrowing capacity	$ 10,000,000.0
Term Debt | London Interbank Offered Rate (LIBOR)
Long-term Purchase Commitment [Line Items]
Basis spread on variable rate	3.60%
Revolving Line of Credit
Long-term Purchase Commitment [Line Items]
Current borrowing capacity	$ 5,000,000.0
Accounts receivable borrowing base percentage	80.00%
Interest rate, stated percentage	5.00%
Minimum cash multiplier | multiplier				6
Revolving Line of Credit | Prime Rate [Member]
Long-term Purchase Commitment [Line Items]
Basis spread on variable rate	1.00%
Demand Deposits [Member]
Long-term Purchase Commitment [Line Items]
Restricted cash and investments, noncurrent					700,000
Eighth Lease Amendment | Subsequent Event
Long-term Purchase Commitment [Line Items]
Renewal term									5 years	88 months
Letters of credit										$ 1,100,000
Fifth Amendment
Long-term Purchase Commitment [Line Items]
Payments for capital improvements							$ 3,600,000
Payments for (proceeds from) tenant allowance								$ (3,100,000)
Amendment 7
Long-term Purchase Commitment [Line Items]
Incentive from lessor				$ 500,000	900,000
Redwood City, California, Penobscot Space
Long-term Purchase Commitment [Line Items]
Lease area space occupancy | ft²				28,200
Redwood City, California, Building 2 Space
Long-term Purchase Commitment [Line Items]
Lease area space occupancy | ft²				37,900
Redwood City, California, 501 Chesapeake Space
Long-term Purchase Commitment [Line Items]
Lease area space occupancy | ft²				11,200
Redwood City, California, Saginaw Space
Long-term Purchase Commitment [Line Items]
Lease area space occupancy | ft²				29,900
Headquarters Redwood City
Long-term Purchase Commitment [Line Items]
Asset retirement obligations				$ 200,000	$ 200,000