CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income
Balance at period start (in shares) at Dec. 31, 2019		53,254
Balance at period start at Dec. 31, 2019	$ 648,242	$ 533	$ 715,069	$ (67,942)	$ 582
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock option / common stock warrants (in shares)		351
Exercise of common stock warrants	3,936	$ 3	3,933
Stock-based compensation (in shares)		296
Stock-based compensation	1,615	$ 3	1,612
Purchase of common stock for retirement (in shares)		(64)
Purchase of common stock for retirement	(1,068)	$ (1)	(1,067)
Net loss	(222,337)			(222,337)
Balance at period end (in shares) at Mar. 31, 2020		53,837
Balance at period end at Mar. 31, 2020	430,388	$ 538	719,547	(290,279)	582
Balance at period start (in shares) at Dec. 31, 2019		53,254
Balance at period start at Dec. 31, 2019	648,242	$ 533	715,069	(67,942)	582
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income	0
Net loss	(262,897)
Balance at period end (in shares) at Jun. 30, 2020		53,942
Balance at period end at Jun. 30, 2020	392,476	$ 539	722,194	(330,839)	582
Balance at period start (in shares) at Mar. 31, 2020		53,837
Balance at period start at Mar. 31, 2020	430,388	$ 538	719,547	(290,279)	582
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for employee stock purchase plan (in shares)		95
Issuance of common stock for employee stock purchase plan	855	$ 1	854
Stock-based compensation (in shares)		10
Stock-based compensation	1,794		1,794
Purchase of common stock for retirement	(1)		(1)
Other comprehensive income	0
Net loss	(40,560)			(40,560)
Balance at period end (in shares) at Jun. 30, 2020		53,942
Balance at period end at Jun. 30, 2020	392,476	$ 539	722,194	(330,839)	582
Balance at period start (in shares) at Dec. 31, 2020		54,003
Balance at period start at Dec. 31, 2020	246,274	$ 540	726,504	(477,028)	(3,742)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock offering, net of issuance costs (in shares)		5,750
Common stock offering, net of issuance costs	87,401	$ 58	87,343
Exercise of stock option / common stock warrants (in shares)		4
Exercise of common stock warrants	58		58
Stock-based compensation (in shares)		461
Stock-based compensation	1,886	$ 3	1,883
Purchase of common stock for retirement (in shares)		(76)
Purchase of common stock for retirement	(1,321)		(1,321)
Other comprehensive income	3,996				3,996
Net loss	(62,227)			(62,227)
Balance at period end (in shares) at Mar. 31, 2021		60,142
Balance at period end at Mar. 31, 2021	276,067	$ 601	814,467	(539,255)	254
Balance at period start (in shares) at Dec. 31, 2020		54,003
Balance at period start at Dec. 31, 2020	246,274	$ 540	726,504	(477,028)	(3,742)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income	3,996
Net loss	(171,185)
Balance at period end (in shares) at Jun. 30, 2021		60,185
Balance at period end at Jun. 30, 2021	169,692	$ 602	817,049	(648,213)	254
Balance at period start (in shares) at Mar. 31, 2021		60,142
Balance at period start at Mar. 31, 2021	276,067	$ 601	814,467	(539,255)	254
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock offering, net of issuance costs	(208)		(208)
Issuance of common stock for employee stock purchase plan (in shares)		42
Issuance of common stock for employee stock purchase plan	714	$ 1	713
Exercise of common stock warrants	0
Stock-based compensation (in shares)		1
Stock-based compensation	2,079		2,079
Purchase of common stock for retirement	(2)		(2)
Other comprehensive income	0
Net loss	(108,958)			(108,958)
Balance at period end (in shares) at Jun. 30, 2021		60,185
Balance at period end at Jun. 30, 2021	$ 169,692	$ 602	$ 817,049	$ (648,213)	$ 254