Borrowings - Notes payable (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Instrument
Notes payable	$ 1,224,230	$ 1,224,981
Advances with FHLB with maturities ranging from 2021 Through 2029
Debt Instrument
Advances with the FHLB	541,469	542,469
Advances with FRB | Fixed rate with maturities on 2022 paying interest annually
Debt Instrument
Long Term Debt	934	1,009
Unsecured senior debt | Fixed Rate with maturities on 2023 paying interest semiannually
Debt Instrument
Long Term Debt	296,891	296,574
Junior subordinated debt | Fixed Rate with maturities ranging from 2033 to 2034
Debt Instrument
Long Term Debt	$ 384,936	$ 384,929