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Debt (Schedule of Additional Information Related to Debt Instruments) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	$ 276.7	$ 123.7	$ 276.7	$ 186.4
Average outstanding balance	178.8	22.2	120.9	39.4
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	263.4	200.1	263.4	200.1
Average outstanding balance	5.8	6.6	5.1	5.5
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	12.0	12.0	12.0	12.0
Average outstanding balance	11.6	12.0	11.8	12.0
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	100.0	100.0	100.0	100.0
Average outstanding balance	28.9	3.3	15.6	2.1
Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	75.0	49.9	75.0	49.9
Average outstanding balance	$ 28.4	$ 1.6	$ 14.8	$ 6.0

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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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No definition available.

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