Other Borrowings and Subordinated Notes and Debentures - Debt Components (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 1,524,030	$ 1,699,400
U.S. Bank National Association | Revolving credit facility
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 0	0
U.S. Bank National Association | Revolving credit facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.50%
Total other borrowings
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 1,169,989	1,345,450
FHLB advances, net of discount, due 2019 to 2033, 1.38% to 7.37% secured by real estate loans
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 1,169,989	1,345,450
FHLB advances, net of discount, due 2019 to 2033, 1.38% to 7.37% secured by real estate loans | Minimum
Debt Instrument [Line Items]
Fixed rate (as percent)		1.38%
FHLB advances, net of discount, due 2019 to 2033, 1.38% to 7.37% secured by real estate loans | Maximum
Debt Instrument [Line Items]
Fixed rate (as percent)		7.37%
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]
Fixed rate (as percent)	5.00%	5.00%
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 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) | 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 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) | 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 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) | 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 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) | 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 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) | 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 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) | 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 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) | 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 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) | 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 and Debentures
Debt Instrument [Line Items]
Unamortized debt issuance costs		$ (3,281)	(3,372)
Total other borrowings and subordinated debt		$ 354,041	$ 353,950