Note 11 - Stockholders' Equity (Details Textual) - USD ($)			12 Months Ended				48 Months Ended
	Jul. 17, 2019	May 15, 2013	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2019
Preferred Stock, Shares Authorized			1,000,000	1,000,000			1,000,000
Preferred Stock, Par or Stated Value Per Share			$ 0.0001	$ 0.0001			$ 0.0001
Common Stock, Shares Authorized			200,000,000	200,000,000			200,000,000
Common Stock, Par or Stated Value Per Share			$ 0.0001	$ 0.0001			$ 0.0001
Class of Warrant or Right, Exercise Price of Warrants or Rights				$ 11.50	$ 11.50
Class of Warrant or Right, Exercised			27,311
Class of Warrant or Right, Outstanding	0			10,088,074	10,656,520
Temporary Equity, Dividends, Adjustment			$ 2,654,000
Stock Repurchased During Period, Value			$ 23,000	$ 854,000	$ 6,192,000
Common Stock [Member]
Stock Repurchased During Period, Shares			1,895	9,030	547,058
Stock Repurchased During Period, Value
Stock and Warrant Repurchase Plan [Member]
Stock Repurchase Program, Additional Number of Shares Authorized to be Repurchased						15,000,000
Stock Repurchase Program, Number of Shares Authorized to be Repurchased						35,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount			$ 12,100,000				$ 12,100,000
Stock and Warrant Repurchase Plan [Member] | Common Stock [Member]
Warrants Repurchased During Period			1,895	568,446	529,867		6,011,926
Warrants Repurchased During Period, Value			$ 23,000	$ 800,000	$ 1,100,000		$ 14,700,000
Stock Repurchased During Period, Shares				9,030	547,058		866,701
Stock Repurchased During Period, Value				$ 100,000	$ 5,100,000		$ 8,200,000
Warrants Issued with Units Sold in Initial Public Offering [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right		1
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 11.50
Warrant Exchange [Member]
Warrant Exchange, Common Stock to be Received	0.385
Class of Warrant or Right, Outstanding	9,935,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	3,824,959
Temporary Equity, Dividends, Adjustment	$ 2,700,000
Warrants Exchanged in Consent Solicitation [Member]
Non Warrant Exchange, Common Stock to be Received	0.36575
Class of Warrant or Right, Outstanding	125,763
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	45,981
IPO [Member]
Common Stock, Par or Stated Value Per Share		$ 0.0001
Units Sold During Period		20,000,000
Shares Issued, Price Per Share		$ 10
Over-allotment Option Sold During Period		2,000,000
Proceeds from Issuance or Sale of Equity, Total		$ 200,000,000
Number of Common Stock in Each Unit		1
Number of Warrants in Each Unit		0.5
Separation of Units Enforced, Period after Merger		30 days
Separation of Units Enforced, Termination Thereafter		5 years