Note 10 - Stock-based Compensation - Summary of 2009 ESPP (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Weighted average per share discount from market value for shares purchased (in dollars per share)	$ 13	$ 15.89	$ 11.92
The 2009 ESPP [Member]
Shares purchased pursuant to 2009 ESPP (in shares)	94,909
Weighted average per share price of shares purchased (in dollars per share)	$ 73.67
Weighted average per share discount from market value for shares purchased (in dollars per share)	$ 13
Shares available for purchase pursuant to 2009 ESPP (in shares)	372,751