FHLB Advances, Other Borrowings and Subordinated Notes (Summary of Debt) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Sep. 18, 2018
Debt Disclosure [Abstract]
FHLB advances	$ 1,228,436	$ 1,228,429	$ 1,174,894
Other borrowings:
Notes payable	96,363	101,710	167,746	$ 150,000
Short-term borrowings	12,416	11,366	12,127
Other	64,659	65,108	66,266
Secured borrowings	343,439	340,744	241,364
Total other borrowings	516,877	518,928	487,503
Subordinated notes	436,595	436,506	436,179
Total FHLB advances, other borrowings and subordinated notes	$ 2,181,908	$ 2,183,863	$ 2,098,576