Note 12 - Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended			36 Months Ended	48 Months Ended
	Nov. 02, 2016	May 15, 2013	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2018
Preferred Stock, Shares Authorized			1,000,000	1,000,000		1,000,000	1,000,000
Preferred Stock, Par or Stated Value Per Share			$ 0.0001	$ 0.0001		$ 0.0001	$ 0.0001
Common Stock, Shares Authorized			200,000,000	200,000,000		200,000,000	200,000,000
Common Stock, Par or Stated Value Per Share			$ 0.0001	$ 0.0001		$ 0.0001	$ 0.0001
Class of Warrant or Right, Exercise Price of Warrants or Rights			$ 11.50	$ 11.50	$ 11.50	$ 11.50	$ 11.50
Stock Repurchased During Period, Value			$ 854	$ 6,192	$ 10,343
Common Stock [Member]
Stock Repurchased During Period, Shares			9,030	547,058	308,718
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
Warrants Repurchased During Period			568,446	529,867	2,821,995	6,011,926
Warrants Repurchased During Period, Value			$ 800	$ 1,100	$ 7,300		$ 14,700
Stock Repurchase Program, Remaining Authorized Repurchase Amount			$ 12,100			$ 12,100	$ 12,100
Stock and Warrant Repurchase Plan [Member] | Common Stock [Member]
Stock Repurchased During Period, Shares			9,030	547,058	308,718	864,806
Stock Repurchased During Period, Value			$ 100	$ 5,100	$ 3,000	$ 8,100
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
Class of Warrant or Right, Redemption Price		0.01
Class of Warrant or Right, Redemption, Stock Price Trigger		24
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
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