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Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended						12 Months Ended
	Dec. 21, 2018	Dec. 31, 2020	May 31, 2020	Oct. 31, 2019	Dec. 31, 2018	Aug. 31, 2018	Sep. 30, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Aug. 06, 2018
Stock transactions
Proceeds from public offering of common stock, net of issuance costs								$ 213,303
Par value (per share)		$ 0.00001						$ 0.00001	$ 0.00001
2017 Form S-3
Stock transactions
Maximum aggregate offering price							$ 200,000
2019 Form S-3
Stock transactions
Maximum aggregate offering price				$ 250,000				$ 94,200
Common Stock
Stock transactions
Price (in dollars per share)		$ 21.00	$ 14.00					$ 21.00
Common stock sold (in shares)		4,761,904	7,000,000					13,526,189
Issuance of common stock upon exercise of Exchange Warrants (in shares)									599,997
Common Stock | 2019 Form S-3
Stock transactions
Common stock sold (in shares)								2,483,719
Proceeds from public offering of common stock, net of issuance costs								$ 41,900
Common Stock | Underwriter overallotment option
Stock transactions
Price (in dollars per share)		$ 21.00	$ 14.00					$ 21.00
Common stock sold (in shares)		714,285	1,050,000
Proceeds from public offering of common stock, net of issuance costs		$ 107,600
Common Stock | Private Placement
Stock transactions
Number of warrants exercised		0						0
Common Stock | 2017 Sales Agreement
Stock transactions
Common stock sold (in shares)								2,846,641		151,273
Proceeds from public offering of common stock, net of issuance costs			$ 105,300					$ 34,500		$ 1,500
At-the-market offering (ATM)
Stock transactions
Maximum aggregate offering price								$ 31,900
At-the-market offering (ATM) | 2019 Form S-3
Stock transactions
Maximum aggregate offering price				$ 75,000
At-the-market offering (ATM) | 2017 Sales Agreement
Stock transactions
Maximum aggregate offering price							$ 50,000
Investors | Common Stock
Stock transactions
Price (in dollars per share)											$ 8.00
Common stock sold (in shares)						2,750,000
Aggregate gross proceeds											$ 21,700
Investors | Common Stock | Private Placement
Stock transactions
Warrants to purchase common stock, number of shares											2,750,000
Exchange Agreement | Exchanging Stockholders
Stock transactions
Warrants to purchase common stock, number of shares	1,000,000
Common stock exchanged for pre-funded warrants					1,000,000
Par value (per share)	$ 0.00001
Exercise Price (per share)	$ 0.00001
Duration of warrants from date of issuance (in years)	10 years
Equity method investment, ownership percentage	9.99%
Exchange Agreement | Exchanging Stockholders | Common Stock
Stock transactions
Number of warrants exercised									600,000
Issuance of common stock upon exercise of Exchange Warrants (in shares)									599,997
Exchange warrants unexercised		400,000						400,000
Group one | Common Stock | Private Placement
Stock transactions
Number of shares to be converted for each warrant											1,375,000
Exercise Price (per share)											$ 10.00
Group two | Common Stock | Private Placement
Stock transactions
Number of shares to be converted for each warrant											1,375,000
Exercise Price (per share)											$ 15.00

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