Note 8 - Loans - Non-accrual Troubled Debt Restructurings (Details) - Non-accruing Troubled Debt Restructuring [Member] - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Accruing TDRs	$ 27,718	$ 30,347	$ 33,416	$ 33,691	$ 30,045	$ 29,722
Payment Deferral [Member]
Accruing TDRs	20,343		20,472
Contractual Interest Rate Reduction [Member]
Accruing TDRs			1,677
Rate Reduction and Payment Deferral [Member]
Accruing TDRs	7,375		11,267
Commercial Portfolio Segment [Member]
Accruing TDRs	14,579		12,944
Commercial Portfolio Segment [Member] | Payment Deferral [Member]
Accruing TDRs	14,579		12,944
Commercial Portfolio Segment [Member] | Contractual Interest Rate Reduction [Member]
Accruing TDRs
Commercial Portfolio Segment [Member] | Rate Reduction and Payment Deferral [Member]
Accruing TDRs
Commercial Real Estate Portfolio Segment [Member]
Accruing TDRs	11,124		19,021
Commercial Real Estate Portfolio Segment [Member] | Payment Deferral [Member]
Accruing TDRs	3,863		6,231
Commercial Real Estate Portfolio Segment [Member] | Contractual Interest Rate Reduction [Member]
Accruing TDRs			1,677
Commercial Real Estate Portfolio Segment [Member] | Rate Reduction and Payment Deferral [Member]
Accruing TDRs	7,261		11,113
Residential Portfolio Segment [Member]
Accruing TDRs	2,015		1,451
Residential Portfolio Segment [Member] | Payment Deferral [Member]
Accruing TDRs	1,901		1,297
Residential Portfolio Segment [Member] | Contractual Interest Rate Reduction [Member]
Accruing TDRs
Residential Portfolio Segment [Member] | Rate Reduction and Payment Deferral [Member]
Accruing TDRs	$ 114		$ 154