Other Borrowings and Subordinated Notes and Debentures - Debt Components (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 1,785,225	$ 1,685,859
Total other borrowings
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		1,396,829	1,297,599
FHLB advances, net of discount, due 2020 to 2034, 0.23% to 7.37% secured by real estate loans
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 1,362,295	1,262,691
FHLB advances, net of discount, due 2020 to 2034, 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 2020 to 2034, 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		$ 34,534	34,908
Total subordinated notes and debentures
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		388,396	388,260
Unamortized debt issuance costs		$ (2,916)	(3,008)
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, net of discount, 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, net of discount, 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, 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]
Long-term debt, gross		$ 10,310	10,310
Subordinated Notes | 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 | 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		$ 25,054	25,015
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		$ 3,009	3,004
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%
Subordinated Notes | Other subordinated debentures, due 12/31/2036, floating rate of prime rate minus 1.1%, reset quarterly | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.10%
Unsecured Debt | Other subordinated debentures, due 12/31/2036, floating rate of prime rate minus 1.1%, reset quarterly
Debt Instrument [Line Items]
Long-term debt, gross		$ 5,927	$ 5,927