Fair Value of Financial Instruments (Schedule of Interest Rate Swaps) (Details) (Interest Rate Swap [Member], USD $)	6 Months Ended
	Jun. 30, 2013
Derivative [Line Items]
Notional Amount	$ 2,800,000,000
Interest Rate Swaps One [Member]
Derivative [Line Items]
Notional Amount	300,000,000
Fixed Interest Rate	5.242%
Termination Date	Aug. 06, 2013
Fair Value of Liability	1,499,000
Interest Rate Swaps Two [Member]
Derivative [Line Items]
Notional Amount	100,000,000
Fixed Interest Rate	5.038%
Termination Date	Aug. 30, 2013
Fair Value of Liability	793,000
Interest Rate Swaps Three [Member]
Derivative [Line Items]
Notional Amount	50,000,000
Fixed Interest Rate	3.586%
Termination Date	Oct. 23, 2013
Fair Value of Liability	521,000
Interest Rate Swaps Four [Member]
Derivative [Line Items]
Notional Amount	50,000,000
Fixed Interest Rate	3.524%
Termination Date	Oct. 23, 2013
Fair Value of Liability	511,000
Interest Rate Swaps Five [Member]
Derivative [Line Items]
Notional Amount	100,000,000
Fixed Interest Rate	5.05%
Termination Date	Nov. 30, 2013
Fair Value of Liability	1,990,000
Interest Rate Swaps Six [Member]
Derivative [Line Items]
Notional Amount	200,000,000
Fixed Interest Rate	2.07%
Termination Date	Dec. 19, 2013
Fair Value of Liability	1,676,000
Interest Rate Swaps Seven [Member]
Derivative [Line Items]
Notional Amount	100,000,000
Fixed Interest Rate	5.231%
Termination Date	Jul. 25, 2014
Fair Value of Liability	5,230,000
Interest Rate Swaps Eight [Member]
Derivative [Line Items]
Notional Amount	100,000,000
Fixed Interest Rate	5.231%
Termination Date	Jul. 25, 2014
Fair Value of Liability	5,230,000
Interest Rate Swaps Nine [Member]
Derivative [Line Items]
Notional Amount	200,000,000
Fixed Interest Rate	5.16%
Termination Date	Jul. 25, 2014
Fair Value of Liability	10,308,000
Interest Rate Swaps Ten [Member]
Derivative [Line Items]
Notional Amount	75,000,000
Fixed Interest Rate	5.041%
Termination Date	Jul. 25, 2014
Fair Value of Liability	3,769,000
Interest Rate Swaps Eleven [Member]
Derivative [Line Items]
Notional Amount	125,000,000
Fixed Interest Rate	5.022%
Termination Date	Jul. 25, 2014
Fair Value of Liability	6,256,000
Interest Rate Swaps Twelve [Member]
Derivative [Line Items]
Notional Amount	100,000,000
Fixed Interest Rate	2.621%
Termination Date	Jul. 25, 2014
Fair Value of Liability	2,424,000
Interest Rate Swaps Thirteen [Member]
Derivative [Line Items]
Notional Amount	100,000,000
Fixed Interest Rate	3.11%
Termination Date	Jul. 25, 2014
Fair Value of Liability	2,950,000
Interest Rate Swaps Fourteen [Member]
Derivative [Line Items]
Notional Amount	100,000,000
Fixed Interest Rate	3.258%
Termination Date	Jul. 25, 2014
Fair Value of Liability	3,109,000
Interest Rate Swaps Fifteen [Member]
Derivative [Line Items]
Notional Amount	200,000,000
Fixed Interest Rate	2.693%
Termination Date	Oct. 26, 2014
Fair Value of Liability	6,120,000
Interest Rate Swaps Sixteen [Member]
Derivative [Line Items]
Notional Amount	300,000,000
Fixed Interest Rate	3.447%
Termination Date	Aug. 08, 2016
Fair Value of Liability	24,066,000
Interest Rate Swaps Seventeen [Member]
Derivative [Line Items]
Notional Amount	200,000,000
Fixed Interest Rate	3.429%
Termination Date	Aug. 19, 2016
Fair Value of Liability	16,010,000
Interest Rate Swaps Eighteen [Member]
Derivative [Line Items]
Notional Amount	100,000,000
Fixed Interest Rate	3.401%
Termination Date	Aug. 19, 2016
Fair Value of Liability	7,923,000
Interest Rate Swaps Nineteen [Member]
Derivative [Line Items]
Notional Amount	200,000,000
Fixed Interest Rate	3.50%
Termination Date	Aug. 30, 2016
Fair Value of Liability	16,546,000
Interest Rate Swaps Twenty [Member]
Derivative [Line Items]
Notional Amount	100,000,000
Fixed Interest Rate	3.005%
Termination Date	Nov. 30, 2016
Fair Value of Liability	$ 6,909,000