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) | London Interbank Offered Rate (LIBOR)

Subordinated Debt | Trust preferred securities, due 12/30/2033, floating rate of 2.80% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)

Subordinated Debt | Trust preferred securities, net of discount, due 6/30/2035, floating rate of 1.75% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)

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 | London Interbank Offered Rate (LIBOR)

Subordinated Debt | Trust preferred securities, net of discount, due 12/5/2033, floating rate of 2.88% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)

Subordinated Debt | Trust preferred securities, net of discount, due 10/18/2034, floating rate of 2.00% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)

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 | London Interbank Offered Rate (LIBOR)

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 | London Interbank Offered Rate (LIBOR)

Subordinated Debt | Trust preferred securities, due 6/26/2033, floating rate of 3.10% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)

Subordinated Debt | Trust preferred securities, due 10/7/2033, floating rate of 2.85% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)

Subordinated Debt | Trust preferred securities, due 9/15/2037, floating rate of 2.00% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)

Other Borrowings and Subordinated Debentures - Long-term Debt 2 (Details)	12 Months Ended
	Dec. 31, 2018	Mar. 31, 2018
U.S. Bank National Association \| Revolving Credit Facility \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.50%
FHLB advances, net of discount, due 2019 to 2033, 1.38% to 7.37% secured by residential real estate loans \| Minimum
Debt Instrument [Line Items]
Debt instrument, interest rate (as percent)	1.38%
FHLB advances, net of discount, due 2019 to 2033, 1.38% to 7.37% secured by residential real estate loans \| Maximum
Debt Instrument [Line Items]
Debt instrument, interest rate (as percent)	7.37%
Notes payable, due 10/15/2020, 3.85%, fixed rate, unsecured
Debt Instrument [Line Items]
Debt instrument, interest rate (as percent)	3.85%
Subordinated Debt
Debt Instrument [Line Items]
Debt instrument, interest rate (as percent)	5.00%	5.00%
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) \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	2.15%
Subordinated Debt \| Trust preferred securities, due 12/30/2033, floating rate of 2.80% above the three month LIBOR rate, reset quarterly, callable without penalty \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	2.80%
Subordinated Debt \| Trust preferred securities, net of discount, due 6/30/2035, floating rate of 1.75% above the three month LIBOR rate, reset quarterly, callable without penalty \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.75%
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 \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.37%
Subordinated Debt \| Trust preferred securities, net of discount, due 12/5/2033, floating rate of 2.88% above the three month LIBOR rate, reset quarterly, callable without penalty \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	2.88%
Subordinated Debt \| Trust preferred securities, net of discount, due 10/18/2034, floating rate of 2.00% above the three month LIBOR rate, reset quarterly, callable without penalty \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	2.00%
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 \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.57%
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 \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.45%
Subordinated Debt \| Trust preferred securities, due 6/26/2033, floating rate of 3.10% above the three month LIBOR rate, reset quarterly, callable without penalty \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	3.10%
Subordinated Debt \| Trust preferred securities, due 10/7/2033, floating rate of 2.85% above the three month LIBOR rate, reset quarterly, callable without penalty \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	2.85%
Subordinated Debt \| Trust preferred securities, due 9/15/2037, floating rate of 2.00% above the three month LIBOR rate, reset quarterly, callable without penalty \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	2.00%