Note 14 - Fair Value of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) - USD ($) $ in Thousands		Mar. 31, 2020		Dec. 31, 2019
Equity securities		$ 18,790		$ 28,005
Warrants		3,210		2,181
Equity Securities, FV-NI		18,790		28,005
Fair Value, Inputs, Level 1 [Member]
Equity securities		18,790		28,005
Equity Securities, FV-NI		18,790		28,005
Fair Value, Inputs, Level 2 [Member]
Equity securities		0		0
Equity Securities, FV-NI		0		0
Fair Value, Inputs, Level 3 [Member]
Equity securities		0		0
Equity Securities, FV-NI		0		0
Estimate of Fair Value Measurement [Member]
Cash and due from banks		136,350		177,240
Short-term investments		363,666		416,538
Securities available-for-sale		1,355,173		1,451,842
Loans, net	[1]	15,588,186		15,444,752
Equity securities		18,790		28,005
Investment in Federal Home Loan Bank stock		17,250		18,090
Deposits		15,133,137		14,719,452
Short-term borrowings		12,898		25,683
Advances from Federal Home Loan Bank		502,934		674,530
Other borrowings		31,323		30,764
Long-term debt		56,317		76,058
Equity Securities, FV-NI		18,790		28,005
Estimate of Fair Value Measurement [Member] | Warrants [Member]
Warrants		24		39
Warrants				39
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and due from banks		136,350		177,240
Short-term investments		363,666		416,538
Securities available-for-sale		0		74,936
Loans, net		0	[1]	0
Equity securities		18,790		28,005
Investment in Federal Home Loan Bank stock		0		0
Deposits		0		0
Short-term borrowings		0		0
Advances from Federal Home Loan Bank		0		0
Other borrowings		0		0
Long-term debt		0		0
Equity Securities, FV-NI		18,790		28,005
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | Warrants [Member]
Warrants		0
Warrants				0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Cash and due from banks		0		0
Short-term investments		0		0
Securities available-for-sale		1,355,173		1,376,906
Loans, net		0	[1]	0
Equity securities		0		0
Investment in Federal Home Loan Bank stock		17,250		18,090
Deposits		0		0
Short-term borrowings		0		0
Advances from Federal Home Loan Bank		502,934		674,530
Other borrowings		0		0
Long-term debt		56,317		76,058
Equity Securities, FV-NI		0		0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Warrants [Member]
Warrants		0
Warrants				0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Cash and due from banks		0		0
Short-term investments		0		0
Securities available-for-sale		0		0
Loans, net		15,588,186	[1]	15,444,752
Equity securities		0		0
Investment in Federal Home Loan Bank stock		0		0
Deposits		15,133,137		14,719,452
Short-term borrowings		12,898		25,683
Advances from Federal Home Loan Bank		0		0
Other borrowings		31,323		30,764
Long-term debt		0		0
Equity Securities, FV-NI		0		0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Warrants [Member]
Warrants		$ 24
Warrants				$ 39

[1] In accordance with the prospective adoption of ASU 2016-01, the fair value of loans as of December 31, 2019 & 2018 was measured using an exit price notion.