Borrowings and Subordinated Debentures - Subordinated Debentures (Details) $ in Thousands, € in Millions		6 Months Ended
		Jun. 30, 2021 USD ($)		Jun. 30, 2021 EUR (€)		Dec. 31, 2020 USD ($)
Subordinated Borrowing [Line Items]
Subordinated Debentures, Gross		$ 936,742				$ 543,275
Subordinated debentures		$ 861,788				$ 465,812
Rate		6.50%		6.50%		0.00%
Trust Preferred Securities Two Thousand Six Series Three
Subordinated Borrowing [Line Items]
Denomination value | €				€ 25.8
Subordinated notes due May 2031
Subordinated Borrowing [Line Items]
Rate Index (Quarterly Reset)		25200.00%
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]	$ (74,954)				$ (77,463)
Rate		2.65%	[2]	2.65%	[2]	2.24%
Subordinated Debentures | Subordinated Debt Trust V Due September 2033
Subordinated Borrowing [Line Items]
Balance		$ 10,310				$ 10,310
Rate		3.22%	[2]	3.22%	[2]	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		3.17%	[2]	3.17%	[2]	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		3.07%	[2]	3.07%	[2]	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		2.94%	[2]	2.94%	[2]	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		1.81%	[2]	1.81%	[2]	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		1.72%	[2]	1.72%	[2]	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		1.67%	[2]	1.67%	[2]	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		2.07%	[2]	2.07%	[2]	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		2.14%	[2]	2.14%	[2]	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		2.14%	[2]	2.14%	[2]	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		2.14%	[2]	2.14%	[2]	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	[3]	$ 30,564				$ 31,487
Rate		1.52%	[2]	1.52%	[2]	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		2.14%	[2]	2.14%	[2]	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		2.14%	[2]	2.14%	[2]	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		2.14%	[2]	2.14%	[2]	2.16%
Date Issued		Jun. 13, 2007
Maturity Date		Jul. 30, 2037
Subordinated Debentures | Subordinated notes due May 2031
Subordinated Borrowing [Line Items]
Balance		$ 394,390	[4]			$ 0
Rate		3.25%	[2]	3.25%	[2]	0.00%
Date Issued		Apr. 30, 2021
Maturity Date		May 01, 2031

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

[2] Rates do not include the effects of discounts and issuance costs.

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

[4] Net of issuance costs of $5.6 million.