Fair Value Measurements (Details Textual) (USD $)	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
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 Securities	6 years 8 months
Amortized cost of the investment in available-for-sale debt securities	62,600,000	59,800,000
Period For Reclassification Into Earnings	12 months
Estimated fair value of consolidated debt	4,200,000,000	4,500,000,000
Total indebtedness	3,962,236,000	4,388,185,000
Cash Flow Hedging [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notional Amount of Interest Rate swaps	50,400,000	50,700,000
Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Average Remaining Maturity of Interest Rate Swaps	6 years 3 months
Amount of unrealized losses estimated to be reclassified from accumulated other comprehensive loss to earnings during the next 12 months	$ 1,700,000
Weighted average fixed rate of interest rate swaps	3.43%