Borrowings - CLO Borrowings (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 EUR (€)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 EUR (€)	Dec. 31, 2019 USD ($)	Feb. 28, 2017 EUR (€)
Debt Instrument [Line Items]
Borrowing Outstanding		$ 1,997.3		$ 1,985.7
CLO Term Loan Maturing November 2031
Debt Instrument [Line Items]
Borrowing Outstanding		$ 77.5	€ 66,100,000	75.3
Debt principal amount | €					€ 66,100,000
CLO Term Loan Maturing November 2031 | Euribor
Debt Instrument [Line Items]
Interest rate		2.33%	2.33%
CLO Term Loan Maturing April 2031
Debt Instrument [Line Items]
Borrowing Outstanding		$ 22.7		22.9
CLO Term Loan Maturing April 2031 | LIBOR
Debt Instrument [Line Items]
Interest rate		2.20%	2.20%
Margin spread on interest rate	1.932%
CLO Term Loan Maturing July 2031
Debt Instrument [Line Items]
Borrowing Outstanding		$ 22.9		22.9
CLO Term Loan Maturing July 2031 | LIBOR
Debt Instrument [Line Items]
Interest rate		2.19%	2.19%
Margin spread on interest rate	1.923%
CLO Term Loan Maturing July 2029
Debt Instrument [Line Items]
Borrowing Outstanding		$ 22.7		22.8
CLO Term Loan Maturing July 2029 | LIBOR
Debt Instrument [Line Items]
Interest rate		2.08%	2.08%
Margin spread on interest rate	1.808%
CLO Term Loan Maturing August 2022
Debt Instrument [Line Items]
Borrowing Outstanding		$ 20.4		19.5
Debt principal amount | €			€ 17,400,000
CLO Term Loan Maturing August 2022 | Euribor
Debt Instrument [Line Items]
Interest rate		1.75%	1.75%
Margin spread on interest rate	1.75%
CLO Term Loan Maturing August 2030
Debt Instrument [Line Items]
Borrowing Outstanding		$ 22.4		22.6
CLO Term Loan Maturing August 2030 | LIBOR
Debt Instrument [Line Items]
Interest rate		2.11%	2.11%
Margin spread on interest rate	1.848%
CLO Term Loan Maturing January 2030
Debt Instrument [Line Items]
Borrowing Outstanding		$ 22.7		22.7
CLO Term Loan Maturing January 2030 | LIBOR
Debt Instrument [Line Items]
Interest rate		2.01%	2.01%
Margin spread on interest rate	1.731%
CLO Term Loan Maturing October 2030
Debt Instrument [Line Items]
Borrowing Outstanding		$ 19.0		19.1
CLO Term Loan Maturing October 2030 | LIBOR
Debt Instrument [Line Items]
Interest rate		1.92%	1.92%
Margin spread on interest rate	1.647%
CLO Term Loan Maturing January 2029
Debt Instrument [Line Items]
Borrowing Outstanding		$ 20.8		20.8
CLO Term Loan Maturing January 2029 | LIBOR
Debt Instrument [Line Items]
Interest rate		1.64%	1.64%
Margin spread on interest rate	1.365%
CLO Term Loan Maturing January 2030
Debt Instrument [Line Items]
Borrowing Outstanding		$ 19.2		19.2
CLO Term Loan Maturing January 2030 | LIBOR
Debt Instrument [Line Items]
Interest rate		1.90%	1.90%
Margin spread on interest rate	1.624%
CLO Term Loan Maturing January 2031
Debt Instrument [Line Items]
Borrowing Outstanding		$ 15.2		15.3
CLO Term Loan Maturing January 2031 | LIBOR
Debt Instrument [Line Items]
Interest rate		1.83%	1.83%
Margin spread on interest rate	1.552%
CLO Term Loan Maturing March 2032
Debt Instrument [Line Items]
Borrowing Outstanding		$ 21.7		20.8
Periodic interest rate adjustment, percent	0.08%
Periodic interest rate adjustment, maximum amount | €	€ 54,120
CLO Term Loan Maturing March 2032 | Average effective interest rate
Debt Instrument [Line Items]
Interest rate		2.63%	2.63%
Margin spread on interest rate	0.50%
CLO Term Loan Maturing August 2032
Debt Instrument [Line Items]
Borrowing Outstanding		$ 21.9		21.0
CLO Term Loan Maturing August 2032 | Average effective interest rate
Debt Instrument [Line Items]
Interest rate		2.52%	2.52%
Margin spread on interest rate	0.50%
CLO Term Loan Maturing April 2033
Debt Instrument [Line Items]
Borrowing Outstanding		$ 20.9		0.0
CLO Term Loan Maturing April 2033 | Average effective interest rate
Debt Instrument [Line Items]
Interest rate		1.59%	1.59%
Margin spread on interest rate	0.50%
CLO Borrowings
Debt Instrument [Line Items]
Borrowing Outstanding		$ 350.0		$ 324.9