Note 13 - Fair Value Measurements and Fair Value of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) - USD ($) $ in Thousands		Mar. 31, 2021	Dec. 31, 2020
Equity securities		$ 20,993	$ 23,744
Warrants		3,615	3,409
Fair Value, Inputs, Level 1 [Member]
Equity securities		20,993	23,744
Fair Value, Inputs, Level 2 [Member]
Equity securities		0	0
Fair Value, Inputs, Level 3 [Member]
Equity securities		0	0
Estimate of Fair Value Measurement [Member]
Cash and due from banks		141,885	138,616
Short-term investments		1,612,411	1,282,462
Securities available-for-sale		908,844	1,036,550
Loans, net	[1]	16,094,374	16,103,471
Equity securities		20,993	23,744
Investment in Federal Home Loan Bank stock		17,250	17,250
Deposits		16,364,101	16,125,808
Advances from Federal Home Loan Bank		77,691	155,133
Other borrowings		19,861	19,632
Long-term debt		64,892	65,487
Estimate of Fair Value Measurement [Member] | Warrants [Member]
Warrants		16	21
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and due from banks		141,885	138,616
Short-term investments		1,612,411	1,282,462
Securities available-for-sale		40,720	80,948
Loans, net	[1]	0	0
Equity securities		20,993	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		868,124	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		77,691	155,133
Other borrowings		0	0
Long-term debt		64,892	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]	16,094,374	16,103,471
Equity securities		0	0
Investment in Federal Home Loan Bank stock		0	0
Deposits		16,364,101	16,125,808
Advances from Federal Home Loan Bank		0	0
Other borrowings		19,861	19,632
Long-term debt		0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Warrants [Member]
Warrants		$ 16	$ 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.