Note 2 - Investments (Details Textual) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Available-for-sale Securities, Debt Securities, Current		$ 33,000		$ 29,100
Payments to Acquire Available-for-sale Securities, Debt		35,300
Proceeds from Sale and Maturity of Marketable Securities		31,169	$ 7,240
Available-for-sale Securities, Equity Securities, Noncurrent		7,100		5,000
Available-for-sale Equity Securities, Amortized Cost Basis		5,700		$ 4,000
Available-for-sale Equity Securities, Acquired During Period, Cost Basis		$ 1,600	$ 900
Other than Temporary Impairment Losses, Investments	$ 1,000