Note 6 - Share-based Compensation - Shared-based Compensation Expense By Plan and the Related Tax Benefit (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based compensation expense	$ 266,000	$ 220,000	$ 1,108,000	$ 1,097,000
Related income tax benefit	58,000	53,000	168,000	172,000
Stock Options and SARs [Member]
Share-based compensation expense	82,000	81,000	747,000	833,000
Restricted Stock [Member]
Share-based compensation expense	80,000	71,000	164,000	151,000
Performance Shares [Member]
Share-based compensation expense	$ 104,000	$ 68,000	$ 197,000	$ 113,000