Related Party Transactions (Debt Agreements) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Related Party [Line Items]
Amount of Notes	$ 1,575,000
Amount of Notes		$ 1,711,000
Prudential Financial Loan 1
Related Party [Line Items]
Amount of Notes	$ 0
Amount of Notes		50,000
Interest Rate	2.64%
Prudential Financial Loan 2
Related Party [Line Items]
Amount of Notes	$ 11,000
Amount of Notes		11,000
Interest Rate	3.61%
Prudential Financial Loan 3
Related Party [Line Items]
Amount of Notes	$ 22,000
Amount of Notes		22,000
Prudential Financial Loan 3 | Minimum
Related Party [Line Items]
Interest Rate	3.32%
Prudential Financial Loan 3 | Maximum
Related Party [Line Items]
Interest Rate	3.61%
Prudential Insurance Loan 1
Related Party [Line Items]
Amount of Notes	$ 204,000
Amount of Notes		204,000
Interest Rate	3.47%
Washington Street Loan 1
Related Party [Line Items]
Amount of Notes	$ 0
Amount of Notes		237,000
Washington Street Loan 1 | Minimum
Related Party [Line Items]
Interest Rate	2.44%
Washington Street Loan 1 | Maximum
Related Party [Line Items]
Interest Rate	3.02%
Washington Street Loan 2
Related Party [Line Items]
Amount of Notes	$ 0
Amount of Notes		198,000
Washington Street Loan 2 | Minimum
Related Party [Line Items]
Interest Rate	1.33%
Washington Street Loan 2 | Maximum
Related Party [Line Items]
Interest Rate	1.87%
Washington Street Loan 3
Related Party [Line Items]
Amount of Notes	$ 0
Amount of Notes		39,000
Washington Street Loan 3 | Minimum
Related Party [Line Items]
Interest Rate	1.33%
Washington Street Loan 3 | Maximum
Related Party [Line Items]
Interest Rate	1.87%
Prudential Financial Loan 4
Related Party [Line Items]
Amount of Notes	$ 9,000
Amount of Notes		9,000
Interest Rate	2.24%
Prudential Financial Loan 5
Related Party [Line Items]
Amount of Notes	$ 23,000
Amount of Notes		23,000
Interest Rate	3.19%
Prudential Insurance Loan 2
Related Party [Line Items]
Amount of Notes	$ 120,000
Amount of Notes		120,000
Interest Rate	2.60%
Prudential Insurance Loan 3
Related Party [Line Items]
Amount of Notes	$ 130,000
Amount of Notes		130,000
Interest Rate	4.39%
Prudential Insurance Loan 4
Related Party [Line Items]
Amount of Notes	$ 250,000
Amount of Notes		250,000
Interest Rate	3.64%
Prudential Insurance Loan 5
Related Party [Line Items]
Amount of Notes	$ 30,000
Amount of Notes		30,000
Interest Rate	1.89%
Prudential Insurance Loan 6
Related Party [Line Items]
Amount of Notes	$ 40,000
Amount of Notes		40,000
Interest Rate	3.95%
Prudential Insurance Loan 7
Related Party [Line Items]
Amount of Notes	$ 20,000
Amount of Notes		20,000
Interest Rate	2.80%
Prudential Insurance Loan 8
Related Party [Line Items]
Amount of Notes	$ 50,000
Amount of Notes		50,000
Interest Rate	3.95%
Prudential Insurance Loan 9
Related Party [Line Items]
Amount of Notes	$ 50,000
Amount of Notes		50,000
Interest Rate	2.80%
Prudential Insurance Loan 10
Related Party [Line Items]
Amount of Notes	$ 100,000
Amount of Notes		100,000
Interest Rate	3.47%
Prudential Insurance Loan 11
Related Party [Line Items]
Amount of Notes	$ 100,000
Amount of Notes		100,000
Interest Rate	3.95%
Prudential Financial Loan 6
Related Party [Line Items]
Amount of Notes	$ 5,000
Amount of Notes		5,000
Interest Rate	2.57%
Prudential Financial Loan 7
Related Party [Line Items]
Amount of Notes	$ 23,000
Amount of Notes		23,000
Interest Rate	3.14%
Prudential Financial Loan 8
Related Party [Line Items]
Amount of Notes	$ 66,000
Amount of Notes		0
Interest Rate	3.52%
Prudential Financial Loan 9
Related Party [Line Items]
Amount of Notes	$ 6,000
Amount of Notes		0
Interest Rate	2.86%
Prudential Financial Loan 10
Related Party [Line Items]
Amount of Notes	$ 158,000
Amount of Notes		0
Prudential Financial Loan 10 | Minimum
Related Party [Line Items]
Interest Rate	1.09%
Prudential Financial Loan 10 | Maximum
Related Party [Line Items]
Interest Rate	1.63%
Prudential Financial Loan 11
Related Party [Line Items]
Amount of Notes	$ 132,000
Amount of Notes		0
Prudential Financial Loan 11 | Minimum
Related Party [Line Items]
Interest Rate	1.40%
Prudential Financial Loan 11 | Maximum
Related Party [Line Items]
Interest Rate	1.93%
Prudential Financial Loan 12
Related Party [Line Items]
Amount of Notes	$ 26,000
Amount of Notes		$ 0
Prudential Financial Loan 12 | Minimum
Related Party [Line Items]
Interest Rate	1.40%
Prudential Financial Loan 12 | Maximum
Related Party [Line Items]
Interest Rate	1.93%