Fair Value Measurements and Derivative Instruments - Credit Features (Details) (USD $) In Thousands, unless otherwise specified			9 Months Ended													9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Moody's, Baa3 Rating	Sep. 30, 2014 Moody's, Ba1 Rating	Sep. 30, 2014 Standard & Poor's, BBB- Rating Minimum	Sep. 30, 2014 Standard & Poor's, BB Rating	Sep. 30, 2014 Interest rate contracts hedge	Sep. 30, 2014 Designated as Hedging Instrument		Dec. 31, 2013 Designated as Hedging Instrument		Sep. 30, 2014 Other long-term Liabilities Designated as Hedging Instrument Interest rate swaps		Dec. 31, 2013 Other long-term Liabilities Designated as Hedging Instrument Interest rate swaps		Sep. 30, 2014 Derivative Maturity More than Five Years Minimum
Derivative Instruments
Credit ratings for senior debt			Baa3	Ba1	BBB-	BB
Maturity of interest rate instrument																5 years
Liability Derivatives	$ 275,036	$ 100,260						$ 252,678	[1]	$ 77,629	[1]	$ 50,688	[1]	$ 66,920	[1]
Number of derivative instruments							5

[1] Accounting Standard Codification 815-20 “Derivatives and Hedging.”