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Debt (Schedule of Additional Information Related to Debt Instruments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	$ 193.3	$ 153.9	$ 282.9	$ 265.4
Average outstanding balance	71.1	22.2	80.1	44.8
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	201.0	201.0	201.0	201.0
Average outstanding balance	126.7	4.4	102.8	4.4
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	0.0	0.0	100.0	99.0
Average outstanding balance	0.0	0.0	1.5	0.7
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	35.0	97.3	35.0	99.0
Average outstanding balance	3.4	2.1	1.2	1.4
Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	0.0	0.0	0.0	75.0
Average outstanding balance	0.0	0.0	0.0	0.5
Warehouse Facility VII [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	50.0	100.0	101.5	150.0
Average outstanding balance	23.9	2.2	9.4	10.4
Warehouse Facility VIII [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	75.0	0.0	75.0	0.0
Average outstanding balance	$ 12.7	$ 0.0	$ 12.7	$ 0.0

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- Definition

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- Definition

Average amount borrowed under the credit facility during the period.

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- Definition

Maximum amount borrowed under the credit facility at any time during the period.

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