Note 7 - Equity Plans - Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs) [Member]	3 Months Ended
	Mar. 31, 2017 $ / shares shares
Outstanding beginning balance (in shares) | shares	421,486
Outstanding beginning balance (in dollars per share) | $ / shares	$ 19.92
Granted (in shares) | shares	50,033
Granted (in dollars per share) | $ / shares	$ 20.47
Converted into shares (in shares) | shares	(2,798)
Converted into shares (in dollars per share) | $ / shares	$ 15.18
Forfeited (in shares) | shares
Forfeited (in dollars per share) | $ / shares
Outstanding ending balance (in shares) | shares	468,721
Outstanding ending balance (in dollars per share) | $ / shares	$ 20.01
Vested (in shares) | shares	426,069
Vested (in dollars per share) | $ / shares	$ 19.73