Note 13 - Fair Value Measurements and Fair Value of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) - USD ($) $ in Thousands		Sep. 30, 2021	Dec. 31, 2020
Securities available-for-sale		$ 1,079,216	$ 1,036,550
Equity securities		20,117	23,744
Warrants		5,187	3,409
Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale		40,211	80,948
Equity securities		20,117	23,744
Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale		1,039,005	955,602
Equity securities		0	0
Fair Value, Inputs, Level 3 [Member]
Securities available-for-sale		0	0
Equity securities		0	0
Estimate of Fair Value Measurement [Member]
Cash and due from banks		156,287	138,616
Short-term investments		1,667,875	1,282,462
Securities available-for-sale		1,079,216	1,036,550
Loans, net	[1]	16,301,993	16,103,471
Equity securities		20,117	23,744
Investment in Federal Home Loan Bank stock		17,250	17,250
Deposits		17,007,694	16,125,808
Advances from Federal Home Loan Bank		20,856	155,133
Other borrowings		19,164	19,632
Long-term debt		62,274	65,487
Estimate of Fair Value Measurement [Member] | Warrants [Member]
Warrants		22	21
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and due from banks		156,287	138,616
Short-term investments		1,667,875	1,282,462
Securities available-for-sale		40,211	80,948
Loans, net	[1]	0	0
Equity securities		20,117	23,744
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
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | Warrants [Member]
Warrants		0	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		1,039,005	955,602
Loans, net	[1]	0	0
Equity securities		0	0
Investment in Federal Home Loan Bank stock		17,250	17,250
Deposits		0	0
Advances from Federal Home Loan Bank		20,856	155,133
Other borrowings		0	0
Long-term debt		62,274	65,487
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Warrants [Member]
Warrants		0	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	[1]	16,301,993	16,103,471
Equity securities		0	0
Investment in Federal Home Loan Bank stock		0	0
Deposits		17,007,694	16,125,808
Advances from Federal Home Loan Bank		0	0
Other borrowings		19,164	19,632
Long-term debt		0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Warrants [Member]
Warrants		$ 22	$ 21

[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.