Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) Customer Segment	Dec. 31, 2016 USD ($) Customer	Dec. 31, 2015 Customer	Dec. 21, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable	$ 8,000,000	$ 0
Restricted cash and cash equivalents	162,000	0
Restricted cash and cash equivalents, long-term	2,500,000
Assets held for sale	0	0
Significant interest or penalties incurred related to income taxes	$ 0
Number of reportable segments | Segment	1
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives	P3Y
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives	P10Y
JDRF [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash and cash equivalents	$ 200,000
Reneo [Member]
Summary Of Significant Accounting Policies [Line Items]
Investments, fair value		$ 0		$ 2,500,000
Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of customers | Customer	4	2	2
Revenue [Member] | Customer [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage	100.00%	100.00%	100.00%