Stockholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended					12 Months Ended
	Jun. 30, 2019	Jan. 31, 2019	Jun. 30, 2018	Nov. 30, 2017	Jan. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Warrants - issued and outstanding
Stock issued in transaction (shares)	2,415,000	1,854,838	3,162,500
Sale price of common stock (USD per share)	$ 97.00	$ 62.00	$ 38.85
Proceeds from sale of common stock	$ 219,900	$ 107,900	$ 130,700
Exercise price of warrants (USD per share)			$ 0.001
Proceeds from disgorgement of stockholders' short-swing profits		$ 1,100				$ 1,050	$ 0	$ 0
Number of warrants exercised via cashless exercises (shares)						2,125,033	0	52,825
Net exercise of warrants (shares)						2,125,000		638,554
Exercise of warrants for cash (shares)								585,729
Proceeds from warrant exercises								$ 4,600
Warrant
Warrants - issued and outstanding
Stock issued in transaction (shares)			421,650	4,137,999	7,258,263
Sale price of common stock (USD per share)			$ 38.849	$ 12.999	$ 5.599
Maximum
Warrants - issued and outstanding
Proportion of common stock owned (as a percent)			9.99%
Minimum
Warrants - issued and outstanding
Proportion of common stock owned (as a percent)			4.99%