Note 14 - Fair Value of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020		Dec. 31, 2019
Equity securities	$ 22,964		$ 28,005
Warrants	3,992		2,181
Equity Securities, FV-NI	22,964		28,005
Fair Value, Inputs, Level 1 [Member]
Equity securities	22,964		28,005
Equity Securities, FV-NI	22,964		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	128,896		177,240
Short-term investments	1,305,170		416,538
Securities available-for-sale	1,080,540		1,451,842
Loans, net	16,030,529	[1]	15,444,752
Equity securities	22,964		28,005
Investment in Federal Home Loan Bank stock	17,250		18,090
Deposits	16,061,257		14,719,452
Advances from Federal Home Loan Bank	238,509		674,530
Other borrowings	19,550		30,764
Long-term debt	64,296		76,058
Equity Securities, FV-NI	22,964		28,005
Short-term borrowings	0		25,683
Estimate of Fair Value Measurement [Member] | Warrants [Member]
Warrants	20		39
Warrants			39
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and due from banks	128,896		177,240
Short-term investments	1,305,170		416,538
Securities available-for-sale	99,980		74,936
Loans, net	0	[1]	0
Equity securities	22,964		28,005
Investment in Federal Home Loan Bank stock	0		0
Deposits	0		0
Advances from Federal Home Loan Bank	0		0
Other borrowings	0		0
Long-term debt	0		0
Equity Securities, FV-NI	22,964		28,005
Short-term borrowings			0
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	980,560		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
Advances from Federal Home Loan Bank	238,509		674,530
Other borrowings	0		0
Long-term debt	64,296		76,058
Equity Securities, FV-NI	0		0
Short-term borrowings			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	16,030,529	[1]	15,444,752
Equity securities	0		0
Investment in Federal Home Loan Bank stock	0		0
Deposits	16,061,257		14,719,452
Advances from Federal Home Loan Bank	0		0
Other borrowings	19,550		30,764
Long-term debt	0		0
Equity Securities, FV-NI	0		0
Short-term borrowings			25,683
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Warrants [Member]
Warrants	$ 20
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.