Note 11 - Stock-based Compensation - Phantom Stock Plan (Details) - Phantom Share Units (PSUs) [Member] - Phantom Stock Plan [Member]	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Outstanding, beginning balance (in shares) | shares	79,440
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 21.64
Granted (in shares) | shares	12,056
Granted (in dollars per share) | $ / shares	$ 20.49
Forfeited (in shares) | shares	0
Forfeited (in dollars per share) | $ / shares	$ 0
Distributions (in shares) | shares	(2,157)
Distributions (in dollars per share) | $ / shares	$ 20.76
Outstanding, ending balance (in shares) | shares	89,339
Outstanding, ending (in dollars per share) | $ / shares	$ 29.39
Vested at December 31, 2016 (in shares) | shares	89,164
Vested at December 31, 2016 (in dollars per share) | $ / shares	$ 29.39