Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($) Customer	Jun. 30, 2018 Customer	Jun. 30, 2019 USD ($) Customer	Jun. 30, 2018 Customer	Dec. 31, 2018 USD ($) Customer
Summary Of Significant Accounting Policies [Line Items]
Contractual liabilities	$ 3,943		$ 3,943		$ 3,184
Percentage of reverse repurchase agreement collateralized received	102.00%		102.00%
Letters of credit outstanding and collateral amount	$ 11,700		$ 11,700		11,200
Inventory reserve	$ 1,200		$ 1,200		$ 700
Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Number of major customers | Customer			0		0
Total Revenue
Summary Of Significant Accounting Policies [Line Items]
Number of major customers | Customer	0	0	0	0
Maximum
Summary Of Significant Accounting Policies [Line Items]
Percentage of reverse repurchase agreement collateralized deposits	102.00%		102.00%
Deferred Revenue
Summary Of Significant Accounting Policies [Line Items]
Contractual liabilities	$ 3,300		$ 3,300		$ 2,700