Fair Value Measurements - Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Document Fiscal Year Focus	2013
Unsecured Credit Facilities [Member] | Minimum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Assumptions, Risk Free Interest Rate	1.40%	1.60%
Unsecured Credit Facilities [Member] | Maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Assumptions, Risk Free Interest Rate	1.40%	1.60%
Notes Receivable [Member] | Minimum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Assumptions, Risk Free Interest Rate	7.75%	7.00%
Notes Receivable [Member] | Maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Assumptions, Risk Free Interest Rate	7.75%	8.10%
Notes Payable to Banks [Member] | Minimum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Assumptions, Risk Free Interest Rate	3.00%	2.40%
Notes Payable to Banks [Member] | Maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Assumptions, Risk Free Interest Rate	3.50%	3.30%
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Receivable, Fair Value	$ 11,600	$ 23,700
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value	1,936,400	2,000,000
Fair Value, Inputs, Level 2 [Member] | Unsecured Credit Facilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	$ 75,400	$ 170,200