Note 2 - Restatement of Consolidated Financial Statements - Effect of Restatement on Financial Statement (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																6 Months Ended				9 Months Ended				12 Months Ended
	Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Mar. 30, 2019		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Mar. 30, 2018		Jun. 30, 2019		Jun. 30, 2018		Sep. 30, 2019		Sep. 30, 2018		Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Warrant liability	$ 41,771		$ 44,194		$ 48,106				$ 50,425		$ 32,599		$ 14,725				$ 44,194		$ 32,599		$ 41,771		$ 50,425		$ 39,602	$ 28,516
Total liabilities	48,598		49,231		51,813				52,944		34,731		16,546				49,231		34,731		48,598		52,944		49,362	30,835
Additional paid in capital																										113,008	$ 63,505
Accumulated deficit	(103,035)		(113,304)		(117,556)				(119,268)	[1]	(94,722)		(68,284)				(113,304)		(94,722)		(103,035)		(119,268)	[1]	(100,052)	(98,395)	(73,051)
Total shareholders’ equity	35,191		2,072		(3,740)				(6,495)		(12,944)		(4,253)				2,072		(12,944)		35,191		(6,495)		43,454	14,632	(9,532)	$ (9,532)
Change in fair value of warrant liability	(1,128)		(3,586)		(19,663)		$ (19,663)		(25,696)		(27,485)		(4,870)		$ 4,870		(16,077)		(22,615)		(14,949)		(48,311)		(12,835)	(28,271)
Total other expense	11,041		3,505		(19,727)				(25,660)		(27,631)		4,733				(16,222)		(22,896)		(5,181)		(48,557)		(2,978)	(28,667)
Net income (loss) before provision for income taxes	10,269		4,252		(19,161)												(14,909)				(4,640)				(3,198)	(25,005)
Net loss (restated)	10,269		4,252		(19,161)		(19,161)		(24,465)		(26,346)		4,873		4,873		(14,909)		(21,472)		(4,640)		(45,938)		(1,657)	(25,005)
Net income (loss) attributable to common stockholders	$ 8,380		$ 3,425		$ (19,161)				$ (24,545)		$ (26,439)		$ 4,767				$ (14,909)		$ (21,672)		$ (4,640)		$ (46,217)		(1,657)	$ (25,344)
Basic net income (loss) per common share (in dollars per share)	$ 0.42		$ 0.18		$ (1.03)				$ (1.42)		$ (1.74)		$ 0.22				$ (0.80)		$ (1.48)		$ (0.24)		$ (2.98)			$ (1.56)
Diluted net income (loss) per common share (in dollars per share)	$ 0.35		$ 0.02		$ (1.03)				$ (1.42)		$ (1.74)		$ (0.02)				$ (0.80)		$ (1.48)		$ (0.24)		$ (2.98)			$ (1.56)
Change in fair value of warrant liability	$ 1,128		$ 3,586		$ 19,663		19,663		$ 25,696		$ 27,485		$ 4,870		(4,870)		$ 16,077		$ 22,615		$ 14,949		$ 48,311		$ 12,835	$ 28,271
Previously Reported [Member]
Warrant liability
Total liabilities	7,266		5,476		3,707				2,519		2,132		1,821				5,476		2,132		7,266		2,519			2,319
Additional paid in capital																										114,160	84,036
Accumulated deficit	(60,450)		(69,766)		(70,604)				(71,864)	[1]	(73,015)		(74,060)				(69,766)		(73,015)		(60,450)		(71,864)	[1]		(71,031)	(73,958)
Total shareholders’ equity	76,962		46,266		44,366				43,930		19,655		10,472				46,266		19,655		76,962		43,930			43,148	10,092
Change in fair value of warrant liability
Total other expense	9,913		(81)		(64)				36		(146)		(137)				(145)		(281)		9,768		(246)			(396)
Net income (loss) before provision for income taxes	9,316		838		427												1,265				10,581					3,266
Net loss (restated)	9,316		838		427		427		1,231		1,139		3		3		1,265		1,143		10,581		2,373			3,266
Net income (loss) attributable to common stockholders	$ 9,316		$ 838		$ 427				$ 1,151		$ 1,046		$ (103)				$ 1,265		$ 943		$ 10,581		$ 2,094			$ 2,927
Basic net income (loss) per common share (in dollars per share)	$ 0.47		$ 0.04		$ 0.02				$ 0.07		$ 0.07		$ (0.01)				$ 0.07		$ 0.06		$ 0.55		$ 0.13			$ 0.18
Diluted net income (loss) per common share (in dollars per share)	$ 0.37		$ 0.03		$ 0.02				$ 0.05		$ 0.05		$ (0.01)				$ 0.05		$ 0.05		$ 0.43		$ 0.10			$ 0.14
Change in fair value of warrant liability
Revision of Prior Period, Adjustment [Member]
Warrant liability	$ 41,771	[1]	$ 44,194	[1]	$ 48,106	[1]			$ 50,425	[1]	$ 32,599	[1]	$ 14,725	[1]			44,194	[1]	32,599	[1]	41,771	[1]	50,425	[1]		28,516
Total liabilities	41,332		43,755		48,106				50,425		32,599		14,725				43,755		32,599		41,332		50,425			28,516
Additional paid in capital																										(1,152)	(20,531)
Accumulated deficit	(42,585)	[1],[2]	(43,538)	[1],[2]	(46,952)	[1]			(47,404)	[1]	(21,707)	[1]	5,776	[1]			(43,538)	[1],[2]	(21,707)	[1]	(42,585)	[1],[2]	(47,404)	[1]		(27,364)	907
Total shareholders’ equity	(41,771)		(44,194)		(48,106)				(50,425)		(32,599)		(14,725)				(44,194)		(32,599)		(41,771)		(50,425)			(28,516)	$ (19,624)
Change in fair value of warrant liability	(1,128)	[1]	(3,586)	[1]	(19,663)	[1]	(19,663)	[1]	(25,696)	[1]	(27,485)	[1]	(4,870)	[1]	4,870	[1]	(16,077)	[1]	(22,615)	[1]	(14,949)	[1]	(48,311)	[1]		(28,271)
Total other expense	1,128		3,586		(19,663)				(25,696)		(27,485)		4,870				(16,077)		(22,615)		(14,949)		(48,311)			(28,271)
Net income (loss) before provision for income taxes	953		3,414		(19,588)												(16,174)				(15,221)					(28,271)
Net loss (restated)	953		3,414		(19,588)		(19,588)	[1]	(25,696)		(27,485)		4,870		4,870	[1]	(16,174)	[1]	(22,615)	[1]	(15,221)	[1]	(48,311)	[1]		(28,271)
Net income (loss) attributable to common stockholders	$ (936)		$ 2,587		$ (19,588)				$ (25,696)		$ (27,485)		$ 4,870				$ (16,174)		$ (22,615)		$ (15,221)		$ (48,311)			$ (28,271)
Basic net income (loss) per common share (in dollars per share)	$ (0.05)		$ 0.14		$ (1.05)				$ (1.49)		$ (1.81)		$ 0.23				$ (0.87)		$ (1.54)		$ (0.79)		$ (3.11)			$ (1.74)
Diluted net income (loss) per common share (in dollars per share)	$ (0.02)		$ (0.01)		$ (1.05)				$ (1.47)		$ (1.79)		$ (0.01)				$ (0.85)		$ (1.53)		$ (0.67)		$ (3.08)			$ (1.70)
Change in fair value of warrant liability	$ 1,128	[1]	$ 3,586	[1]	$ 19,663	[1]	$ 19,663	[1]	$ 25,696	[1]	$ 27,485	[1]	$ 4,870	[1]	$ (4,870)	[1]	$ 16,077	[1]	$ 22,615	[1]	$ 14,949	[1]	$ 48,311	[1]		$ 28,271

[1] Adjustments related to recording certain warrants as liabilities, see Note 2: "Restatement of Consolidated Financial Statements".

[2] Adjustments related to change in valuation method of market-based restricted stock awards.