Debt Warehouse Facilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Document Period End Date	Dec. 31, 2020
Line of Credit Facility, Maximum Borrowing Capacity	$ 64.7
Warehouse Agreement Borrowings [Member]
Line of Credit Facility [Line Items]
Unamortized Debt Issuance Expense	$ 1.2	$ 0.9
Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate During Period	1.60%	3.00%
Line of Credit Facility, Average Outstanding Amount	$ 865.1	$ 851.6
Pricing on the Facility based on market rates	LIBOR plus 0.875% to 1.35%
Line of Credit Facility, Maximum Borrowing Capacity	$ 2,750.0
Unamortized Debt Issuance Expense	8.7	12.3
Agreement expires September 21, 2020, Extension [Member]
Line of Credit Facility [Line Items]
Line of Credit, Current	144.4	104.4
Line of Credit Facility, Maximum Borrowing Capacity	$ 400.0	375.0
Agreement expires September 21, 2020, Extension [Member] [Member] [Member]
Line of Credit Facility [Line Items]
Pricing on the Facility based on market rates	LIBOR plus 1.40%
Agreement expires September 19, 2020, Extension [Member]
Line of Credit Facility [Line Items]
Pricing on the Facility based on market rates	LIBOR plus 1.40%
Line of Credit, Current	$ 768.9	184.8
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,600.0	775.0
Agreement expires August 31, 2020 [Member]
Line of Credit Facility [Line Items]
Pricing on the Facility based on market rates	LIBOR plus 1.40%
Line of Credit, Current	$ 195.9	11.4
Line of Credit Facility, Maximum Borrowing Capacity	900.0	100.0
Fannie Mae ASAP program [Member]
Line of Credit Facility [Line Items]
Line of Credit, Current	$ 128.8	53.6
Debt Instrument, Interest Rate Terms	LIBOR plus 1.15%
Line of Credit, Gross [Member]
Line of Credit Facility [Line Items]
Line of Credit, Current	$ 1,499.6	516.8
Line of Credit Facility, Maximum Borrowing Capacity	$ 3,200.0	2,425.0
PNC Agreement- HFF, Extension [Member] [Member]
Line of Credit Facility [Line Items]
Pricing on the Facility based on market rates	LIBOR plus 1.50%
Line of Credit, Current	$ 261.6	151.6
Line of Credit Facility, Maximum Borrowing Capacity	$ 300.0	1,000.0
Huntington Agreement- HFF, Extension [Member] [Member] [Member]
Line of Credit Facility [Line Items]
Pricing on the Facility based on market rates	LIBOR plus 1.25%
Line of Credit, Current	$ 0.0	11.0
Line of Credit Facility, Maximum Borrowing Capacity	$ 0.0	$ 175.0