Note 17 - Employee Benefit Plans (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Minimum Number of Years Allowed to Participate in Employee Stock Ownership Plan	2 years
Stock Issued During Period, Shares, Employee Stock Ownership Plan	16,458	19,377	18,012
Stock Issued During Period, Value, Employee Stock Ownership Plan	$ 646,000	$ 600,000	$ 541,000
Employee Stock Ownership Plan (ESOP), Shares Contributed to ESOP	57,014	103,367	107,202
Employee Stock Ownership Plan (ESOP), Shares in ESOP	865,167
Percentage of Outstanding Common Stock under Employee Stock Ownership Plan	1.10%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	75.00%
Defined Contribution Plan, Employers Matching Contribution, Vesting Percentage, Less Than Two Years of Service	0.00%
Defined Contribution Plan, Employers Matching Contribution, Vesting Percentage, After Two Years of Service	25.00%
Defined Contribution Plan, Employers Matching Contribution, Vesting Percentage, After Two Years of Service, Increment	25.00%
Defined Contribution Plan, Employers Matching Contribution, Vesting Percentage, After Five Years of Service	100.00%
Defined Contribution Plan, Employer Matching, Percentage of Eligible Compensation, After One Year of Service	4.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 2,300,000	$ 2,100,000	$ 2,000,000
Percentage of Participant Borrowing Capacity of Vested Amount	50.00%
Maximum [Member]
Employee Stock Ownership Plan (ESOP), Debt Structure, Direct Loan, Employer Cash Payments Used for Debt Service	$ 50,000
Minimum [Member]
Employee Stock Ownership Plan (ESOP), Debt Structure, Direct Loan, Employer Cash Payments Used for Debt Service	$ 1,000