Fair Value Measurements -Narratives (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt fair value	$ 637,300,000	$ 1,161,900,000
Reported Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt fair value	632,900,000	1,154,000,000
Credit facility | Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Face amount	150,000,000
Interest rate	1.0425%
Credit facility | Swap | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate cash flow hedge liability at fair value	$ 1,000,000	$ 1,800,000