Borrowings and Subordinated Debentures - Subordinated Debentures (Details) $ in Thousands, € in Millions		3 Months Ended
		Mar. 31, 2021 USD ($)	Mar. 31, 2021 EUR (€)	Dec. 31, 2020 USD ($)
Subordinated Borrowing [Line Items]
Subordinated Debentures, Gross		$ 542,022		$ 543,275
Subordinated debentures		$ 465,814		$ 465,812
Rate		4.86%	4.86%	0.00%
Trust Preferred Securities Two Thousand Six Series Three
Subordinated Borrowing [Line Items]
Denomination value | €			€ 25.8
London Interbank Offered Rate (LIBOR) | Subordinated Debt Trust V Due September 2033
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		3.10%
London Interbank Offered Rate (LIBOR) | Subordinated Debt Trust VI Due September 2033
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		3.05%
London Interbank Offered Rate (LIBOR) | Subordinated Debt Trust CII Due September 2033
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		2.95%
London Interbank Offered Rate (LIBOR) | Subordinated Debt Trust VII Due April 2034
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		2.75%
London Interbank Offered Rate (LIBOR) | Subordinated Debt Trust CIII Due September 2035
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		1.69%
London Interbank Offered Rate (LIBOR) | Subordinated Debt Trust FCCI Due March 2037
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		1.60%
London Interbank Offered Rate (LIBOR) | Subordinated Debt Trust FCBI Due December 2035
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		1.55%
London Interbank Offered Rate (LIBOR) | Trust Preferred Securities Two Thousand Five Series One
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		1.95%
London Interbank Offered Rate (LIBOR) | Trust Preferred Securities Two Thousand Five Series Two
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		1.95%
London Interbank Offered Rate (LIBOR) | Two Thousand Six One Term Debt Securitization
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		1.95%
London Interbank Offered Rate (LIBOR) | Two Thousand Six Two Term Debt Securitization
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		1.95%
London Interbank Offered Rate (LIBOR) | Trust Preferred Securities Two Thousand Six Series Four
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		1.95%
London Interbank Offered Rate (LIBOR) | Trust Preferred Securities Two Thousand Six Series Five
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		1.95%
London Interbank Offered Rate (LIBOR) | Two Thousand Seven One Term Debt Securitization
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		1.95%
Euribor Rate | Trust Preferred Securities Two Thousand Six Series Three
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		2.05%
Subordinated Debentures
Subordinated Borrowing [Line Items]
Unamortized discount	[1]	$ (76,208)		$ (77,463)
Rate		2.23%	2.23%	2.24%
Subordinated Debentures | Subordinated Debt Trust V Due September 2033
Subordinated Borrowing [Line Items]
Balance		$ 10,310		$ 10,310
Rate		3.28%	3.28%	3.33%
Date Issued		Aug. 15, 2003
Maturity Date		Sep. 17, 2033
Subordinated Debentures | Subordinated Debt Trust VI Due September 2033
Subordinated Borrowing [Line Items]
Balance		$ 10,310		$ 10,310
Rate		3.23%	3.23%	3.27%
Date Issued		Sep. 03, 2003
Maturity Date		Sep. 15, 2033
Subordinated Debentures | Subordinated Debt Trust CII Due September 2033
Subordinated Borrowing [Line Items]
Balance		$ 5,155		$ 5,155
Rate		3.13%	3.13%	3.18%
Date Issued		Sep. 17, 2003
Maturity Date		Sep. 17, 2033
Subordinated Debentures | Subordinated Debt Trust VII Due April 2034
Subordinated Borrowing [Line Items]
Balance		$ 61,856		$ 61,856
Rate		2.96%	2.96%	2.96%
Date Issued		Feb. 05, 2004
Maturity Date		Apr. 23, 2034
Subordinated Debentures | Subordinated Debt Trust CIII Due September 2035
Subordinated Borrowing [Line Items]
Balance		$ 20,619		$ 20,619
Rate		1.87%	1.87%	1.91%
Date Issued		Aug. 15, 2005
Maturity Date		Sep. 15, 2035
Subordinated Debentures | Subordinated Debt Trust FCCI Due March 2037
Subordinated Borrowing [Line Items]
Balance		$ 16,495		$ 16,495
Rate		1.78%	1.78%	1.82%
Date Issued		Jan. 25, 2007
Maturity Date		Mar. 15, 2037
Subordinated Debentures | Subordinated Debt Trust FCBI Due December 2035
Subordinated Borrowing [Line Items]
Balance		$ 10,310		$ 10,310
Rate		1.73%	1.73%	1.77%
Date Issued		Sep. 30, 2005
Maturity Date		Dec. 15, 2035
Subordinated Debentures | Trust Preferred Securities Two Thousand Five Series One
Subordinated Borrowing [Line Items]
Balance		$ 82,475		$ 82,475
Rate		2.13%	2.13%	2.17%
Date Issued		Nov. 21, 2005
Maturity Date		Dec. 15, 2035
Subordinated Debentures | Trust Preferred Securities Two Thousand Five Series Two
Subordinated Borrowing [Line Items]
Balance		$ 128,866		$ 128,866
Rate		2.16%	2.16%	2.16%
Date Issued		Dec. 14, 2005
Maturity Date		Jan. 30, 2036
Subordinated Debentures | Two Thousand Six One Term Debt Securitization
Subordinated Borrowing [Line Items]
Balance		$ 51,545		$ 51,545
Rate		2.16%	2.16%	2.16%
Date Issued		Feb. 22, 2006
Maturity Date		Apr. 30, 2036
Subordinated Debentures | Two Thousand Six Two Term Debt Securitization
Subordinated Borrowing [Line Items]
Balance		$ 51,550		$ 51,550
Rate		2.16%	2.16%	2.16%
Date Issued		Sep. 27, 2006
Maturity Date		Oct. 30, 2036
Subordinated Debentures | Trust Preferred Securities Two Thousand Six Series Three
Subordinated Borrowing [Line Items]
Balance	[2]	$ 30,234		$ 31,487
Rate		1.51%	1.51%	1.54%
Date Issued		Sep. 29, 2006
Maturity Date		Oct. 30, 2036
Subordinated Debentures | Trust Preferred Securities Two Thousand Six Series Four
Subordinated Borrowing [Line Items]
Balance		$ 16,470		$ 16,470
Rate		2.16%	2.16%	2.16%
Date Issued		Dec. 05, 2006
Maturity Date		Jan. 30, 2037
Subordinated Debentures | Trust Preferred Securities Two Thousand Six Series Five
Subordinated Borrowing [Line Items]
Balance		$ 6,650		$ 6,650
Rate		2.16%	2.16%	2.16%
Date Issued		Dec. 19, 2006
Maturity Date		Jan. 30, 2037
Subordinated Debentures | Two Thousand Seven One Term Debt Securitization
Subordinated Borrowing [Line Items]
Balance		$ 39,177		$ 39,177
Rate		2.16%	2.16%	2.16%
Date Issued		Jun. 13, 2007
Maturity Date		Jul. 30, 2037

[1] Amount represents the fair value adjustment on trust preferred securities assumed in acquisitions.

[2] Denomination is in Euros with a value of €25.8 million.