Note 14 - Fair Value of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) - USD ($) $ in Thousands		Jun. 30, 2020		Dec. 31, 2019
Equity securities		$ 24,570		$ 28,005
Warrants		3,842		2,181
Equity Securities, FV-NI		24,570		28,005
Fair Value, Inputs, Level 1 [Member]
Equity securities		24,570		28,005
Equity Securities, FV-NI		24,570		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		148,700		177,240
Short-term investments		1,425,001		416,538
Securities available-for-sale		1,146,102		1,451,842
Loans, net	[1]	15,954,278		15,444,752
Equity securities		24,570		28,005
Investment in Federal Home Loan Bank stock		17,250		18,090
Deposits		16,334,769		14,719,452
Advances from Federal Home Loan Bank		241,047		674,530
Other borrowings		33,040		30,764
Long-term debt		61,913		76,058
Equity Securities, FV-NI		24,570		28,005
Short-term borrowings		0		25,683
Estimate of Fair Value Measurement [Member] | Warrants [Member]
Warrants		13		39
Warrants				39
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and due from banks		148,700		177,240
Short-term investments		1,425,001		416,538
Securities available-for-sale		99,927		74,936
Loans, net		0	[1]	0
Equity securities		24,570		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		24,570		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		1,046,175		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		241,047		674,530
Other borrowings		0		0
Long-term debt		61,913		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		15,954,278	[1]	15,444,752
Equity securities		0		0
Investment in Federal Home Loan Bank stock		0		0
Deposits		16,334,769		14,719,452
Advances from Federal Home Loan Bank		0		0
Other borrowings		33,040		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		$ 13
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.