Note 6 - Share-based Compensation - Significant Assumptions for Share-based Compensation Awards (Details) - $ / shares		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Expected award (Year)				5 years
Stock Appreciation Rights (SARs) [Member]
Exercise price (in dollars per share)		$ 16.97	$ 16.35	$ 16.97	$ 16.35
Market price (in dollars per share)				$ 16.97	$ 16.35
Risk free interest rate	[1]			1.90%	1.30%
Expected award (Year)	[2]			5 years
Expected volatility	[3]			36.60%	36.50%
Expected dividend yield	[4]			2.10%	2.00%
Employee Stock Option [Member]
Exercise price (in dollars per share)		21.63	16.47	$ 21.63	$ 16.47
Market price (in dollars per share)		$ 21.63	$ 16.47
Risk free interest rate	[1]	1.80%	1.10%
Expected award (Year)	[2]	5 years
Expected volatility	[3]	37.20%	37.10%
Expected dividend yield	[4]	1.80%	2.10%
Employee Stock Option [Member] | Minimum [Member]
Exercise price (in dollars per share)		$ 16.97	$ 16.35	16.97	16.35
Market price (in dollars per share)				$ 16.97	$ 16.35
Risk free interest rate				1.80%	1.10%	[1]
Expected award (Year)	[2]			5 years
Expected volatility	[3]			36.60%	36.50%
Expected dividend yield	[4]			1.80%	1.80%
Employee Stock Option [Member] | Maximum [Member]
Exercise price (in dollars per share)		$ 21.63	$ 18.55	$ 21.63	$ 18.55
Market price (in dollars per share)				$ 21.63	$ 18.55
Risk free interest rate	[1]			2.40%	1.80%
Expected award (Year)	[2]			10 years
Expected volatility	[3]			41.40%	40.30%
Expected dividend yield	[4]			2.10%	2.10%

[1] The risk-free interest rate is based on the yield of a U.S. treasury bond with a similar maturity as the expected life of the awards.

[2] The expected life in years for awards granted was based on the historical exercise patterns experienced by the Company when the award is made.

[3] The determination of expected stock price volatility for awards granted in each of the periods ending September 30, 2017 and 2016 was based on historical prices of Superior's common stock over a period commensurate with the expected life.

[4] The dividend yield assumption is based on the history and expectation of the Company's dividend payouts.