Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jan. 01, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Accounting Policies [Abstract]
Unrealized gains (loss) on short-term investments		$ 3,000	$ 0	$ 21,000	$ 0
Restricted cash		868,000		868,000		$ 0
Operating lease right-of-use assets	$ 39,900,000	115,961,000		115,961,000
Operating lease liability	42,100,000	$ 121,459,000		$ 121,459,000
Reclassification of deferred and prepaid rents to right of use assets	$ 2,200,000