Fair Value (Narrative) (Details) (Senior Notes, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Senior Unsecured Notes due 2019
Fair Value Disclosure [Line Items]
Market discount rate	6.00%	6.00%
Estimated fair value of senior unsecured notes	$ 350.0	$ 350.0
Senior Unsecured Notes due 2021
Fair Value Disclosure [Line Items]
Market discount rate	5.875%	5.875%
Estimated fair value of senior unsecured notes	$ 300.0	$ 300.0