Note 8 - Loans - Non-accrual Troubled Debt Restructurings (Details) - Non-accruing Troubled Debt Restructuring [Member] - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Accruing TDRs	$ 30,347	$ 31,195	$ 33,416	$ 30,045	$ 32,779	$ 29,722
Payment Deferral [Member]
Accruing TDRs	19,767		20,472
Rate Reduction and Payment Deferral [Member]
Accruing TDRs	10,580		11,267
Contractual Interest Rate Reduction [Member]
Accruing TDRs			1,677
Commercial Portfolio Segment [Member]
Accruing TDRs	13,721		12,944
Commercial Portfolio Segment [Member] | Payment Deferral [Member]
Accruing TDRs	13,721		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	14,398		19,021
Commercial Real Estate Portfolio Segment [Member] | Payment Deferral [Member]
Accruing TDRs	3,936		6,231
Commercial Real Estate Portfolio Segment [Member] | Rate Reduction and Payment Deferral [Member]
Accruing TDRs	10,462		11,113
Commercial Real Estate Portfolio Segment [Member] | Contractual Interest Rate Reduction [Member]
Accruing TDRs			1,677
Residential Portfolio Segment [Member]
Accruing TDRs	2,228		1,451
Residential Portfolio Segment [Member] | Payment Deferral [Member]
Accruing TDRs	2,110		1,297
Residential Portfolio Segment [Member] | Rate Reduction and Payment Deferral [Member]
Accruing TDRs	$ 118		154
Residential Portfolio Segment [Member] | Contractual Interest Rate Reduction [Member]
Accruing TDRs