Note 11 - Borrowings and Financing Activities Schedule of Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Advances from Federal Home Loan Banks	$ 173,760	$ 134,875
Senior Notes
Debt Instrument [Line Items]
Senior Notes	887,584	887,110
Senior Notes \| Senior Notes Due 2024
Debt Instrument [Line Items]
Senior Notes	$ 444,707	$ 444,445
Debt Instrument, Interest Rate, Stated Percentage	4.50%	4.50%
Senior Notes \| Senior Notes Due 2027
Debt Instrument [Line Items]
Senior Notes	$ 442,877	$ 442,665
Debt Instrument, Interest Rate, Stated Percentage	4.875%	4.875%
FHLB Advances
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year	$ 97,902
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	24,000	$ 79,002
Long-term Debt, Maturities, Repayments of Principal in Year Two	16,925	19,000
Long-term Debt, Maturities, Repayments of Principal in Year Three	14,994	11,925
Long-term Debt, Maturities, Repayments of Principal in Year Four	9,954	14,994
Long-term Debt, Maturities, Repayments of Principal in Year Five	9,985	9,954
Long-term Debt, Maturities, Repayments of Principal after Year Five		0
Advances from Federal Home Loan Banks	$ 173,760	$ 134,875

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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