Other Borrowings and Subordinated Notes and Debentures - Debt Components (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Mar. 31, 2018	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 1,721,863	$ 1,724,941
FHLB advances, net of discount, due 2022 to 2035, 0.23% to 7.37% secured by real estate loans
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 1,306,360	1,308,674
FHLB advances, net of discount, due 2022 to 2035, 0.23% to 7.37% secured by real estate loans | Minimum
Debt Instrument [Line Items]
Fixed rate (as percent)		0.23%
FHLB advances, net of discount, due 2022 to 2035, 0.23% to 7.37% secured by real estate loans | Maximum
Debt Instrument [Line Items]
Fixed rate (as percent)		7.37%
Other long-term debt
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 32,225	33,393
Total other borrowings
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 1,338,585	1,342,067
Subordinated Notes
Debt Instrument [Line Items]
Fixed rate (as percent)	5.00%	5.00%
Subordinated Notes | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)	2.15%
Subordinated Notes | 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]
Long-term debt, gross		$ 330,000	330,000
Subordinated Notes | 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) | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		2.15%
Subordinated Notes | Trust preferred securities, due 9/15/2037, floating rate of 1.37% above the three month LIBOR rate, reset quarterly
Debt Instrument [Line Items]
Long-term debt, gross		$ 10,310	10,310
Subordinated Notes | Trust preferred securities, due 9/15/2037, floating rate of 1.37% above the three month LIBOR rate, reset quarterly | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.37%
Subordinated Notes | Trust preferred securities, due 6/6/2037, floating rate of 1.57% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 10,310	10,310
Subordinated Notes | Trust preferred securities, due 6/6/2037, floating rate of 1.57% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.57%
Subordinated Notes | 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]
Long-term debt, gross		$ 6,702	6,702
Subordinated Notes | Trust preferred securities, due 12/15/2035, floating rate of 1.45% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.45%
Subordinated Notes | 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]
Long-term debt, gross		$ 25,290	25,172
Subordinated Notes | 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 | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.85%
Subordinated Notes | 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]
Long-term debt, gross		$ 3,036	3,023
Subordinated Notes | 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 | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.85%
Total subordinated notes and debentures
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 383,278	382,874
Unamortized debt issuance costs		$ (2,370)	$ (2,643)