Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	3 Months Ended					12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2017	Dec. 31, 2015	Dec. 31, 2014
Summary Of Significant Accounting Policies [Line Items]
Revenue recognized	$ 2,414,000	$ 198,000	$ 5,000	$ 111,000	$ 17,000	$ 476,000	$ 133,000
Unrecognized excess tax benefits which was fully offset by increase in valuation allowance	$ 28,377,000		$ 13,505,000			28,377,000	$ 13,505,000		$ 24,010,000	$ 7,275,000
Unrecognized tax benefits related to interest or penalties						0
Accounting Standards Update 2014-09 | New Accounting Pronouncement, Early Adoption, Effect
Summary Of Significant Accounting Policies [Line Items]
Revenue recognized						$ 100,000
Accounting Standards Update 2016-09
Summary Of Significant Accounting Policies [Line Items]
Unrecognized excess tax benefits which was fully offset by increase in valuation allowance								$ 19,700,000