Debt (Details 3) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Senior notes | Carrying Value
Notes and other indebtedness
Amount outstanding	$ 330.0	$ 330.0
Senior notes | Estimated Fair Value
Notes and other indebtedness
Amount outstanding	354.5	349.5
Senior notes - Series B | Carrying Value
Notes and other indebtedness
Amount outstanding	105.0	105.0
Senior notes - Series B | Estimated Fair Value
Notes and other indebtedness
Amount outstanding	108.1	108.5
Senior notes - Series C | Carrying Value
Notes and other indebtedness
Amount outstanding	65.0	65.0
Senior notes - Series C | Estimated Fair Value
Notes and other indebtedness
Amount outstanding	68.7	68.2
Senior notes - Series D | Carrying Value
Notes and other indebtedness
Amount outstanding	160.0	160.0
Senior notes - Series D | Estimated Fair Value
Notes and other indebtedness
Amount outstanding	$ 177.7	$ 172.8