Note 12 - Share-based Compensation - Summary of Significant Assumptions for Share-based Compensation Awards (Details) - $ / shares		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Expected award life (Year)		5 years
Stock Appreciation Rights (SARs) [Member]
Exercise price (in dollars per share)		$ 23.59	$ 16.97	$ 16.35
Market price (in dollars per share)		$ 23.59	$ 16.97	$ 16.35
Risk free interest rate	[1]	2.60%	1.90%	1.30%
Expected award life (Year)	[2]	3 years	5 years	5 years
Expected volatility	[3]	38.10%	36.60%	36.50%
Expected dividend yield	[4]	1.60%	2.10%	2.00%
Employee Stock Option [Member] | Minimum [Member]
Exercise price (in dollars per share)		$ 18.86	$ 16.97	$ 16.35
Market price (in dollars per share)		$ 18.86	$ 16.97	$ 16.35
Risk free interest rate	[1]	2.60%	1.80%	1.10%
Expected award life (Year)	[2]	3 years	5 years	5 years
Expected volatility	[3]	35.40%	36.60%	36.50%
Expected dividend yield	[4]	1.60%	1.80%	1.80%
Employee Stock Option [Member] | Maximum [Member]
Exercise price (in dollars per share)		$ 24.28	$ 21.63	$ 18.55
Market price (in dollars per share)		$ 24.28	$ 21.63	$ 18.55
Risk free interest rate	[1]	2.90%	2.40%	1.80%
Expected award life (Year)	[2]	10 years	10 years	10 years
Expected volatility	[3]	42.10%	41.40%	40.30%
Expected dividend yield	[4]	2.10%	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 three years ended December 31, 2018, 2017 and 2016 was based on historical Superior common stock prices 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.