Note 5 - Reconciliation of Common Shareholders' Equity, Common Shares and Earnings Per Share - Reconciliation of Company's Common Shares (Details)	6 Months Ended
	Jun. 30, 2018 shares
Common Shares Outstanding, beginning balance (in shares)	39,557,491
Issuances:
Executive Stock Performance Awards (2015 shares earned) (in shares)	114,648
Vesting of Restricted Stock Units (in shares)	19,950
Restricted Stock Issued to Directors (in shares)	18,200
Directors Deferred Compensation (in shares)	578
Retirements:
Shares Withheld for Individual Income Tax Requirements (in shares)	(59,431)
Common Shares Outstanding, ending balance (in shares)	39,651,436