Other Borrowings and Subordinated Debentures - Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total other borrowings and subordinated debt	$ 1,685,859	$ 1,699,400
Total other borrowings
Debt Instrument [Line Items]
Total other borrowings and subordinated debt	1,297,599	1,345,450
FHLB advances, net of discount, due 2020 to 2033, 0.55% to 7.37%, secured by real estate loans
Debt Instrument [Line Items]
Total other borrowings and subordinated debt	1,262,691	1,345,450
Other long-term debt
Debt Instrument [Line Items]
Total other borrowings and subordinated debt	34,908	0
Total subordinated notes and debentures
Debt Instrument [Line Items]
Unamortized debt issuance costs	(3,008)	(3,372)
Total other borrowings and subordinated debt	388,260	353,950
Subordinated Debt | Subordinated notes payable, due 4/1/2028, fixed-to-floating rate (fixed rate of 5.00% through 3/31/2023, floating rate of 2.15% above the three month LIBOR rate, reset quarterly)
Debt Instrument [Line Items]
Total other borrowings and subordinated debt, gross	330,000	330,000
Subordinated Debt | Trust preferred securities, net of discount, due 9/15/2037, floating rate of 1.37% above the three month LIBOR rate, reset quarterly
Debt Instrument [Line Items]
Total other borrowings and subordinated debt, gross	10,310	10,310
Subordinated Debt | Trust preferred securities, net of discount, due 6/6/2037, floating rate of 1.57% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Total other borrowings and subordinated debt, gross	10,310	10,310
Subordinated Debt | Trust preferred securities, due 12/15/2035, floating rate of 1.45% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Total other borrowings and subordinated debt, gross	6,702	6,702
Subordinated Debt | Trust preferred securities, net of discount, due 6/15/2037, floating rate of 1.85% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Total other borrowings and subordinated debt, gross	25,015	0
Subordinated Debt | Trust preferred securities, net of discount, due 12/15/2036, floating rate of 1.85% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Total other borrowings and subordinated debt, gross	3,004	0
Unsecured Debt | Other subordinated debentures, due 12/31/36, floating rate of prime rate minus 1.1%, reset quarterly
Debt Instrument [Line Items]
Total other borrowings and subordinated debt, gross	$ 5,927	$ 0