Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes receivable	$ 10,480		$ 10,480		$ 10,480
Notes payable	1,364,200		1,364,200		1,699,771
Unsecured credit facilities	263,421		263,421		164,514
Provision for impairment	0	$ 0	(1,666)	$ 0
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	29,280		29,280		29,093
Available-for-sale Securities	8,017		8,017		7,922
Interest Rate Derivative Assets, at Fair Value	476		476
Total	37,773		37,773		37,015
Derivative instruments, at fair value	(1,637)		(1,637)		(20,539)
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities held in trust					0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	29,280		29,280		29,093
Available-for-sale Securities	0		0		0
Interest Rate Derivative Assets, at Fair Value	0		0
Total	29,280		29,280		29,093
Derivative instruments, at fair value	0		0		0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes Payable, Fair Value	1,478,100		1,478,100		1,793,200
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	0		0		0
Available-for-sale Securities	8,017		8,017		7,922
Interest Rate Derivative Assets, at Fair Value	476		476
Total	8,493		8,493		7,922
Derivative instruments, at fair value	(1,637)		(1,637)		(20,539)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes Receivable, Fair Value	10,460		10,460		10,620
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	0		0		0
Available-for-sale Securities	0		0		0
Interest Rate Derivative Assets, at Fair Value	0		0
Total	0		0		0
Derivative instruments, at fair value	0		$ 0		$ 0
Unsecured Credit Facilities [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Risk Free Interest Rate			1.50%		1.10%
Unsecured Credit Facilities [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Risk Free Interest Rate			1.50%		1.10%
Unsecured Credit Facilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unsecured credit facilities, Fair Value	$ 264,800		$ 264,800		$ 165,300
Notes Payable, Other Payables [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Risk Free Interest Rate			2.70%		2.80%
Notes Payable, Other Payables [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Risk Free Interest Rate			3.80%		4.20%
Notes Receivable [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Risk Free Interest Rate			6.80%		6.30%
Notes Receivable [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Risk Free Interest Rate			6.80%		6.30%