Note 12 - Pension and Other Postretirement Benefit Plans (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 1995
Defined Benefit Plan, Benefit Obligation	$ 22,769,000	$ 22,764,000	$ 24,097,000
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	0.00%	0.00%	0.00%
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	$ 1,190,000
Trust for Benefit of Employees [Member]
Full Time Employment, Years of Service	1 year
Amount Borrowed from the Company By the Employee Benefit Trust				$ 7,900,000
Stock Issued During Period, Value, Employee Benefit Plan				$ 7,000
Stock Issued During Period, Shares, Employee Benefit Plan				2,328,750
Employer Contributions to the 401(k) and Profit Sharing Plans Funded By the Employee Benefit Trust	$ 2,800,000	$ 2,800,000	$ 2,700,000
Retirement Plan [Member]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	7.25%	7.50%	7.50%
Retirement Plan [Member] | Savings Bank [Member]
Defined Benefit Plan, Benefit Obligation	$ 22,800,000	$ 22,800,000
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	7.00%
Defined Benefit Plan, Contributions by Employer	$ 0	0	$ 0
Retirement Plan [Member] | Savings Bank [Member] | U.S. Small-cap Blend [Member]
Pension Plan Assets, Equity Securities Held in Mutual Funds, Minimum Market Capitalization	$ 100,000,000
Retirement Plan [Member] | Savings Bank [Member] | Equity Securities [Member]
Defined Benefit Plan, Target Plan Asset Allocations	60.00%
Retirement Plan [Member] | Savings Bank [Member] | Fixed Income Securities [Member]
Defined Benefit Plan, Target Plan Asset Allocations	40.00%
Retirement Plan [Member] | Minimum [Member]
Defined Benefit Plan, Benefit Service Period	3 years
Retirement Plan [Member] | Minimum [Member] | Savings Bank [Member] | U.S. Large-Cap Growth [Member]
Number of StocksHeld in Portfolio	55
Retirement Plan [Member] | Minimum [Member] | Savings Bank [Member] | U.S. Small-cap Blend [Member]
Number of StocksHeld in Portfolio	40
Retirement Plan [Member] | Minimum [Member] | Savings Bank [Member] | International Blend [Member]
Number of StocksHeld in Portfolio	80
Retirement Plan [Member] | Minimum [Member] | Savings Bank [Member] | Equity Securities [Member]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	8.00%
Retirement Plan [Member] | Minimum [Member] | Savings Bank [Member] | Fixed Income Securities [Member]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	3.00%
Retirement Plan [Member] | Maximum [Member]
Defined Benefit Plan, Benefit Service Period	10 years
Retirement Plan [Member] | Maximum [Member] | Savings Bank [Member] | U.S. Large-Cap Growth [Member]
Number of StocksHeld in Portfolio	70
Retirement Plan [Member] | Maximum [Member] | Savings Bank [Member] | U.S. Small-cap Blend [Member]
Number of StocksHeld in Portfolio	100
Retirement Plan [Member] | Maximum [Member] | Savings Bank [Member] | International Blend [Member]
Number of StocksHeld in Portfolio	90
Retirement Plan [Member] | Maximum [Member] | Savings Bank [Member] | Equity Securities [Member]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	10.00%
Retirement Plan [Member] | Maximum [Member] | Savings Bank [Member] | Fixed Income Securities [Member]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	5.00%
Postretirement Plans [Member]
Defined Benefit Plan, Benefit Obligation	$ 7,978,000	7,977,000	8,073,000
Number of Unfunded Postretirement Benefit Plans	2
Full Time Employment, Years of Service	5 years
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	$ 215,000
Defined Benefit Plan, Contributions by Employer	$ 65,000	63,000
Postretirement Plan 1 [Member]
Cost Sharing Arrangement, Medical Benefits Percentage	50.00%
Medical Premiums, Required Percentage to Be Paid By Spouses of Future Retirees	100.00%
The 401(k) Plan [Member]
Defined Contribution Plan, Service Period Requirement	1 year
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage	20.00%
Defined Contribution Plan, Vesting Period	5 years
Defined Contribution Plan, Employer's Matching Contribution, Vesting Percentage, Upon Change of Control	100.00%
Defined Contribution Plan, Cost Recognized	$ 3,300,000	3,000,000	3,100,000
The 401(k) Plan [Member] | Savings Bank [Member]
Defined Contribution Plan, Annual Employer Matching of Employees Contribution, Percent	50.00%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	3.00%
Defined Contribution Retirement Plan ("DCRP") [Member] | Savings Bank [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	4.00%
Non-qualified Deferred Compensation Plan [Member]
Defined Contribution Plan, Service Period Requirement	1 year
Defined Contribution Plan, Annual Employer Matching of Employees Contribution, Percent	50.00%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	5.00%
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage	20.00%
Defined Contribution Plan, Vesting Period	5 years
Defined Contribution Plan, Employer's Matching Contribution, Vesting Percentage, Upon Change of Control	100.00%
Defined Contribution Plan, Cost Recognized	$ 400,000	400,000	400,000
Defined Benefit Plan, Assets for Plan Benefits	10,400,000	10,600,000
Directors' Plan [Member]
Defined Benefit Plan, Benefit Obligation	2,462,000	$ 2,530,000	$ 2,663,000
Full Time Employment, Years of Service		5 years
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	288,000
Defined Benefit Plan, Contributions by Employer	$ 144,000	$ 144,000
Directors' Plan [Member] | In Event of Termination [Member]
Defined Benefit Contributions, Months of Benefit Used in Lump Sum Payment	10 years
Directors' Plan [Member] | Savings Bank [Member]
Defined Benefit Plan, Benefit Obligation		2,500,000
Defined Benefit Plan, Assets for Plan Benefits	$ 4,200,000	$ 4,200,000
Defined Benefit Plan, Contributions by Employer	$ 48,000