Note 9 - Stock-based Compensation - Phantom Stock Plan (Details) - Phantom Share Units (PSUs) [Member] - Phantom Stock Plan [Member]	9 Months Ended
	Sep. 30, 2016 $ / shares shares
Outstanding at December 31, 2015 (in shares) | shares	79,440
Outstanding at December 31, 2015 (in dollars per share) | $ / shares	$ 21.64
Granted (in shares) | shares	11,543
Granted (in dollars per share) | $ / shares	$ 20.09
Forfeited (in shares) | shares
Forfeited (in dollars per share) | $ / shares
Distributions (in shares) | shares	(1,364)
Distributions (in dollars per share) | $ / shares	$ 20.28
Outstanding at September 30, 2016 (in shares) | shares	89,619
Outstanding at September 30, 2016 (in dollars per share) | $ / shares	$ 23.72
Vested at September 30, 2016 (in shares) | shares	89,435
Vested at September 30, 2016 (in dollars per share) | $ / shares	$ 23.72