Note 8 - Loans - Non-accrual Troubled Debt Restructurings (Details) - Non-accruing Troubled Debt Restructuring [Member] - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Accruing TDRs	$ 31,195	$ 33,416	$ 32,779	$ 29,722
Payment Deferral [Member]
Accruing TDRs	20,173	20,472
Rate Reduction and Payment Deferral [Member]
Accruing TDRs	11,022	11,267
Contractual Interest Rate Reduction [Member]
Accruing TDRs		1,677
Commercial Portfolio Segment [Member]
Accruing TDRs	14,568	12,944
Commercial Portfolio Segment [Member] | Payment Deferral [Member]
Accruing TDRs	14,568	12,944
Commercial Portfolio Segment [Member] | Rate Reduction and Payment Deferral [Member]
Accruing TDRs
Commercial Portfolio Segment [Member] | Contractual Interest Rate Reduction [Member]
Accruing TDRs
Commercial Real Estate Portfolio Segment [Member]
Accruing TDRs	14,882	19,021
Commercial Real Estate Portfolio Segment [Member] | Payment Deferral [Member]
Accruing TDRs	4,011	6,231
Commercial Real Estate Portfolio Segment [Member] | Rate Reduction and Payment Deferral [Member]
Accruing TDRs	10,871	11,113
Commercial Real Estate Portfolio Segment [Member] | Contractual Interest Rate Reduction [Member]
Accruing TDRs		1,677
Residential Portfolio Segment [Member]
Accruing TDRs	1,745	1,451
Residential Portfolio Segment [Member] | Payment Deferral [Member]
Accruing TDRs	1,594	1,297
Residential Portfolio Segment [Member] | Rate Reduction and Payment Deferral [Member]
Accruing TDRs	$ 151	154
Residential Portfolio Segment [Member] | Contractual Interest Rate Reduction [Member]
Accruing TDRs