Fair Value of Financial Instruments (Narrative) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Jul. 31, 2014	Apr. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of debt	$ 1,600,000,000	$ 1,700,000,000
Long-term Debt	1,585,867,000	1,663,226,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of debt	1,100,000,000	1,300,000,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of debt	548,200,000	390,100,000
Secured Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	$ 1,600,000,000		$ 140,000,000	$ 2