Note 6 - Share-based Compensation - Shared-based Compensation Expense and the Related Tax Benefit (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based compensation expense	$ 546,000	$ 498,000	$ 1,654,000	$ 1,595,000
Related income tax benefit	29,000	28,000	197,000	200,000
Stock Options and SARs [Member]
Share-based compensation expense	345,000	238,000	1,092,000	1,071,000
Restricted Stock [Member]
Share-based compensation expense	80,000	78,000	243,000	229,000
Performance Shares [Member]
Share-based compensation expense	$ 121,000	$ 182,000	$ 319,000	$ 295,000