Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2015

Fair Value Disclosures [Abstract]

Summary of balance sheet fair values

All financial instruments of the Company are reflected in the accompanying Consolidated Balance Sheets at amounts which, in management's estimation, reasonably approximate their fair values, except for the following:

	June 30, 2015			December 31, 2014
(in thousands)	Carrying Amount		Fair Value	Carrying Amount		Fair Value
Financial assets:
Notes receivable	$	12,281	12,165	$	12,132	11,980
Financial liabilities:
Notes payable	$	1,868,700	1,990,000	$	1,946,357	2,116,000
Unsecured credit facilities	$	120,000	120,000	$	75,000	75,000

Fair Value, Interest rate ranges [Table Text Block]

	June 30, 2015		December 31, 2014
	Low	High	Low	High
Notes receivable	7.3%	7.3%	7.4%	7.4%
Notes payable	1.6%	3.8%	0.9%	3.4%
Unsecured credit facilities	1.1%	1.2%	1.3%	1.3%

Summary of assets measured on recurring basis

	Fair Value Measurements as of June 30, 2015
(in thousands)				Quoted Prices in Active Markets for Identical Assets	Significant Other Observable Inputs		Significant Unobservable Inputs
Assets	Balance			(Level 1)	(Level 2)		(Level 3)
Trading securities held in trust	$	29,530		29,530	—		—
Available-for-sale securities	7,900			—	7,900		—
Interest rate derivatives	168			—	168		—
Total	$	37,598		29,530	8,068		—
Liabilities
Interest rate derivatives	$	(14,183	)	—	(14,183	)	—

	Fair Value Measurements as of December 31, 2014
(in thousands)				Quoted Prices in Active Markets for Identical Assets	Significant Other Observable Inputs		Significant Unobservable Inputs
Assets	Balance			(Level 1)	(Level 2)		(Level 3)
Trading securities held in trust	$	28,134		28,134	—		—
Liabilities
Interest rate derivatives	$	(18,794	)	—	(18,794	)	—