Note 9 - Fair Value Measurements - Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands		Jun. 30, 2024		Dec. 31, 2023
Debt securities available for sale		$ 3,699,318		$ 3,999,801
Agency Residential MBS [Member]
Debt securities available for sale		222,806		239,454
US Government Agencies Debt Securities [Member]
Debt securities available for sale		291,206		294,919
US States and Political Subdivisions Debt Securities [Member]
Debt securities available for sale		69,758		71,283
Corporate Debt Securities [Member]
Debt securities available for sale		1,855,618		1,909,548
US Treasury Securities [Member]
Debt securities available for sale		4,820
Fair Value, Recurring [Member]
Debt securities available for sale		3,699,318		3,999,801
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Debt securities available for sale		4,820		0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Debt securities available for sale		3,694,498		3,999,801
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Debt securities available for sale		0	[1]	0	[2]
Fair Value, Recurring [Member] | Agency Residential MBS [Member]
Debt securities available for sale		222,806		239,454
Fair Value, Recurring [Member] | Agency Residential MBS [Member] | Fair Value, Inputs, Level 1 [Member]
Debt securities available for sale		0		0
Fair Value, Recurring [Member] | Agency Residential MBS [Member] | Fair Value, Inputs, Level 2 [Member]
Debt securities available for sale		222,806		239,454
Fair Value, Recurring [Member] | Agency Residential MBS [Member] | Fair Value, Inputs, Level 3 [Member]
Debt securities available for sale		0	[1]	0	[2]
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member]
Debt securities available for sale		291,206		294,919
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Debt securities available for sale		0		0
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Debt securities available for sale		291,206		294,919
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Debt securities available for sale		0	[1]	0	[2]
Fair Value, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]
Debt securities available for sale		69,758		71,283
Fair Value, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Debt securities available for sale		0		0
Fair Value, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Debt securities available for sale		69,758		71,283
Fair Value, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Debt securities available for sale		0	[1]	0	[2]
Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Debt securities available for sale		1,855,618		1,909,548
Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Debt securities available for sale		0		0
Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Debt securities available for sale		1,855,618		1,909,548
Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Debt securities available for sale		0	[1]	0	[2]
Fair Value, Recurring [Member] | Collateralized Loan Obligations [Member]
Debt securities available for sale		1,255,110		1,484,597
Fair Value, Recurring [Member] | Collateralized Loan Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Debt securities available for sale		0		0
Fair Value, Recurring [Member] | Collateralized Loan Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Debt securities available for sale		1,255,110		1,484,597
Fair Value, Recurring [Member] | Collateralized Loan Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Debt securities available for sale		0	[1]	$ 0	[2]
Fair Value, Recurring [Member] | US Treasury Securities [Member]
Debt securities available for sale		4,820
Fair Value, Recurring [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Debt securities available for sale		4,820
Fair Value, Recurring [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Debt securities available for sale		0
Fair Value, Recurring [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Debt securities available for sale	[1]	$ 0

[1] There were no transfers into or out of level 3 during the six months ended June 30, 2024.

[2] There were no transfers into or out of level 3 during the year ended December 31, 2023.