Fair Value Measurements (Details Textual) (USD $)					3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Cash Flow Hedging [Member]	Dec. 31, 2013 Cash Flow Hedging [Member]	Mar. 31, 2014 Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Face value of available-for-sale securities	$ 100,900,000
Excepted remaining term of available-for-sale debt securities	7 years 2 months
Amortized cost of the investment in available-for-sale debt securities	60,700,000	59,800,000
Derivative Liability, Notional Amount			50,600,000	50,700,000
Derivative, Average Remaining Maturity					6 years 9 months
Period for reclassification of earnings	12 months
Amount of unrealized losses estimated to be reclassified from accumulated other comprehensive loss to earnings during the next 12 months					(1,700,000)
Derivative, Average Fixed Interest Rate					3.43%
Estimated fair value of consolidated debt	4,600,000,000	4,500,000,000
Total indebtedness	$ 4,394,823,000	$ 4,388,185,000