Debt (Summary Of Additional Information Of Credit facilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Revolving Secured Line Of Credit [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	$ 276.7	$ 186.4
Average outstanding balance	80.3	30.8
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	275.0	200.1
Average outstanding balance	4.0	3.8
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	12.0	12.0
Average outstanding balance	5.9	12.0
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	100.0	100.0
Average outstanding balance	7.8	1.6
Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	75.0	49.9
Average outstanding balance	7.8	3.3
Warehouse Facility VII [Member]
Debt Instrument [Line Items]
Maximum outstanding balance	0.0	0.0
Average outstanding balance	$ 0.0	$ 0.0