Commitments and Contingencies - Textual (Details)		1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended	24 Months Ended
	Jun. 30, 2017 USD ($) multiplier	Apr. 30, 2017 USD ($)	Feb. 28, 2017 USD ($)	Jun. 30, 2019 USD ($) ft² building	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) ft² building	Jun. 30, 2018 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2012 USD ($)	Feb. 28, 2019	Jan. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2016
Commitments and Contingencies [Line Items]
Area of real estate property | ft²				107,200		107,200
Number of buildings leased | building				4		4
Accretion expense related to asset retirement obligation				$ 0	$ 0	$ 0	$ 0
Incentive from lessor				0		0							$ 500,000
Asset retirement obligations				200,000		200,000							200,000
Rent expense				1,100,000	800,000	2,300,000	1,600,000
Operating lease, sublease rentals				300,000	$ 300,000	500,000	$ 600,000
Capital lease obligations incurred		$ 300,000	$ 400,000
Term of contract		3 years	3 years											3 years
Right-of-use assets, operating leases, net				25,240,000		25,240,000							0
Operating lease, liability				26,830,000		26,830,000							0
Right-of-use assets - finance leases, net				384,000		384,000						$ 500,000	0
Finance lease, liability				183,000		183,000						300,000	0
Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Loss contingency accrual				0		0
Term Loan [Member]
Commitments and Contingencies [Line Items]
Borrowing capacity	$ 10,000,000.0
Maximum borrowing capacity											$ 1,100,000
Term Loan [Member] | LIBOR [Member]
Commitments and Contingencies [Line Items]
Basis spread on variable rate	3.60%
Revolving Credit Facility [Member]
Commitments and Contingencies [Line Items]
Borrowing capacity	$ 5,000,000.0
Accounts receivable borrowing base percentage	80.00%
Stated interest rate	5.00%
Minimum cash multiplier | multiplier	6
Revolving Credit Facility [Member] | Prime Rate [Member]
Commitments and Contingencies [Line Items]
Basis spread on variable rate	1.00%
Accounting Standards Update 2016-02 [Member]
Commitments and Contingencies [Line Items]
Right-of-use assets, operating leases, net												26,617,000
Operating lease, liability												27,562,000
Right-of-use assets - finance leases, net												493,000
Finance lease, liability												$ 302,000
Demand Deposits [Member]
Commitments and Contingencies [Line Items]
Non-current restricted cash				$ 1,100,000		$ 1,100,000							$ 700,000
Eighth Lease Amendment [Member]
Commitments and Contingencies [Line Items]
Renewal term										88 months
Payments for capital improvements								$ 3,600,000
Tenant reimbursements									$ 3,100,000
Redwood City, California, Penobscot Space [Member]
Commitments and Contingencies [Line Items]
Area of real estate property | ft²				28,200		28,200
Redwood City, California, Building 2 Space [Member]
Commitments and Contingencies [Line Items]
Area of real estate property | ft²				37,900		37,900
Redwood City, California, 501 Chesapeake Space [Member]
Commitments and Contingencies [Line Items]
Area of real estate property | ft²				11,200		11,200
Redwood City, California, Saginaw Space [Member]
Commitments and Contingencies [Line Items]
Area of real estate property | ft²				29,900		29,900