Note 9 - Stock-based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Outstanding balance at December 31, 2016 (in shares)	5,191,000
Outstanding balance at December 31, 2016 (in dollars per share)	$ 17.35
Outstanding balance at March 31, 2017 (Year)	4 years 277 days
Outstanding balance at March 31, 2017	$ 20,130
Expected to vest at March 31, 2017 (in shares)	1,540,000
Expected to vest at March 31, 2017 (in dollars per share)	$ 15.01
Expected to vest at March 31, 2017 (Year)	5 years 189 days
Expected to vest at March 31, 2017	$ 8,431
Exercisable at March 31, 2017 (in shares)	2,920,000
Exercisable at March 31, 2017 (in dollars per share)	$ 18.99
Exercisable at March 31, 2017 (Year)	4 years 76 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0
Granted, Weighted Average Exercise Price (in dollars per share)
Exercised, Shares (in shares)	677	9,975
Exercised, Weighted Average Exercise Price (in dollars per share)	$ 2.71
Exercisable at March 31, 2017	$ 8,231
Forfeitures, Shares (in shares)	(52,000)
Forfeitures, Weighted Average Exercise Price (in dollars per share)	$ 18.88
Expired, Shares (in shares)	(16,000)
Expired, Weighted Average Exercise Price (in dollars per share)	$ 24.87
Outstanding balance at March 31, 2017 (in shares)	5,124,000
Outstanding balance at March 31, 2017 (in dollars per share)	$ 17.32