Note 10 - Pension and Other Postretirement Benefit Plans (Details Textual) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
DirectorsPlanMember
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		$ 300,000
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		300,000
Defined Benefit Plan, Contributions by Employer	$ 36,000
Other Postretirement Benefit Plan [Member]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		200,000
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		$ 200,000
Defined Benefit Plan, Contributions by Employer	$ 18,000