Condensed Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Total
Balance at Dec. 31, 2018	$ 27	$ 677,511	$ (598,101)	$ (319)	$ 79,118
Balance (in shares) at Dec. 31, 2018	26,824,859
Increase (Decrease) in Stockholders' Equity
Exercise of stock options		1,669			1,669
Exercise of stock options (in shares)	80,218
Vesting of restricted stock units (in shares)	3,125
Stock-based compensation		6,636			6,636
Other comprehensive gain (loss)				208	208
Net income (loss)			87,379		87,379
Balance at Mar. 31, 2019	$ 27	685,816	(510,722)	(111)	175,010
Balance (in shares) at Mar. 31, 2019	26,908,202
Balance at Dec. 31, 2018	$ 27	677,511	(598,101)	(319)	79,118
Balance (in shares) at Dec. 31, 2018	26,824,859
Increase (Decrease) in Stockholders' Equity
Net income (loss)					33,158
Balance at Jun. 30, 2019	$ 27	694,266	(564,943)	(16)	129,334
Balance (in shares) at Jun. 30, 2019	27,036,652
Balance at Mar. 31, 2019	$ 27	685,816	(510,722)	(111)	175,010
Balance (in shares) at Mar. 31, 2019	26,908,202
Increase (Decrease) in Stockholders' Equity
Exercise of stock options		1,887			1,887
Exercise of stock options (in shares)	115,612
Exercise of warrants (in shares)	5,813
Vesting of restricted stock units (in shares)	7,025
Stock-based compensation		6,563			6,563
Other comprehensive gain (loss)				95	95
Net income (loss)			(54,221)		(54,221)
Balance at Jun. 30, 2019	$ 27	694,266	(564,943)	(16)	129,334
Balance (in shares) at Jun. 30, 2019	27,036,652
Balance at Dec. 31, 2019	$ 27	715,166	(695,266)	23	$ 19,950
Balance (in shares) at Dec. 31, 2019	27,497,911				27,497,911
Increase (Decrease) in Stockholders' Equity
Exercise of stock options	$ 1	1,013			$ 1,014
Exercise of stock options (in shares)	40,133
Vesting of restricted stock units (in shares)	10,089
Stock-based compensation		7,053			7,053
Other comprehensive gain (loss)				(14)	(14)
Net income (loss)			(78,249)		(78,249)
Balance at Mar. 31, 2020	$ 28	723,232	(773,515)	9	(50,246)
Balance (in shares) at Mar. 31, 2020	27,548,133
Balance at Dec. 31, 2019	$ 27	715,166	(695,266)	23	$ 19,950
Balance (in shares) at Dec. 31, 2019	27,497,911				27,497,911
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)					200,157
Net income (loss)					$ 46,362
Balance at Jun. 30, 2020	$ 28	734,365	(648,904)		$ 85,489
Balance (in shares) at Jun. 30, 2020	27,751,655				27,751,655
Balance at Mar. 31, 2020	$ 28	723,232	(773,515)	9	$ (50,246)
Balance (in shares) at Mar. 31, 2020	27,548,133
Increase (Decrease) in Stockholders' Equity
Exercise of stock options		3,738			3,738
Exercise of stock options (in shares)	160,024
Vesting of restricted stock units (in shares)	43,498
Stock-based compensation		7,395			7,395
Other comprehensive gain (loss)				$ (9)	(9)
Net income (loss)			124,611		124,611
Balance at Jun. 30, 2020	$ 28	$ 734,365	$ (648,904)		$ 85,489
Balance (in shares) at Jun. 30, 2020	27,751,655				27,751,655