Note 12 - Borrowings and Financing Activities - Schedule of Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Advances from Federal Home Loan Banks	$ 138,833	$ 176,483
Senior Notes
Debt Instrument [Line Items]
Senior Notes	1,406,603	1,405,674
Senior Notes \| Senior Notes Due 2024
Debt Instrument [Line Items]
Senior Notes	445,787	445,512
Senior Notes \| Senior Notes Due 2025
Debt Instrument [Line Items]
Senior Notes	517,065	516,634
Senior Notes \| Senior Notes Due 2027
Debt Instrument [Line Items]
Senior Notes	443,751	443,528
FHLB Advances
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year	26,850
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	61,050	67,500
Long-term Debt, Maturities, Repayments of Principal in Year Two	27,995	61,050
Long-term Debt, Maturities, Repayments of Principal in Year Three	9,954	27,995
Long-term Debt, Maturities, Repayments of Principal in Year Four	9,984	9,954
Long-term Debt, Maturities, Repayments of Principal in Year Five	3,000	9,984
Long-term Debt, Maturities, Repayments of Principal after Year Five		0
Advances from Federal Home Loan Banks	$ 138,833	$ 176,483

Amount of borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages.

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