Debt (Details) (USD $)	9 Months Ended		12 Months Ended					9 Months Ended	12 Months Ended				9 Months Ended										9 Months Ended			9 Months Ended			12 Months Ended			9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2010	Dec. 31, 2013	Sep. 30, 2014 Senior Notes [Member]	Sep. 30, 2014 Line of Credit [Member]	Sep. 30, 2014 Unsecured Term Loan [Member]	Sep. 30, 2014 6% Convertible Guaranteed Note [Member]	Dec. 31, 2010 6% Convertible Guaranteed Note [Member]	Dec. 31, 2013 6% Convertible Guaranteed Note [Member]	Sep. 30, 2013 6% Convertible Guaranteed Note [Member]	Jun. 30, 2013 4.25% Senior Note [Member]	Sep. 30, 2014 Other Debt Obligations [Member]	Sep. 30, 2013 Other Debt Obligations [Member]	Sep. 30, 2014 Minimum [Member]	Dec. 31, 2013 Minimum [Member]	Sep. 30, 2014 Maximum [Member]	Dec. 31, 2013 Maximum [Member]	May 31, 2014 Senior Notes Due 2024 [Member] Senior Notes [Member]	Jun. 30, 2013 Senior Notes Due 2023 [Member] Senior Notes [Member]	Sep. 30, 2014 Unsecured Revolving Credit Facility, Expiring February 2018 [Member]	Sep. 30, 2014 Unsecured Revolving Credit Facility, Expiring February 2018 [Member] Unsecured Revolving Credit Facility [Member]	Sep. 30, 2014 Unsecured Revolving Credit Facility, Expiring February 2018 [Member] Minimum [Member]	Sep. 30, 2014 Unsecured Revolving Credit Facility, Expiring February 2018 [Member] Maximum [Member]	Sep. 30, 2014 Unsecured Revolving Credit Facility, Expiring January 2019 [Member] Unsecured Term Loan [Member]	Sep. 30, 2014 Unsecured Revolving Credit Facility, Expiring January 2019 [Member] Minimum [Member] Unsecured Term Loan [Member]	Sep. 30, 2014 Unsecured Revolving Credit Facility, Expiring January 2019 [Member] Maximum [Member] Unsecured Term Loan [Member]	Sep. 30, 2014 Term Loan Facility from Key Bank [Member]	Dec. 31, 2013 Term Loan Facility from Key Bank [Member] Unsecured Term Loan [Member]	Dec. 31, 2013 Term Loan Facility from Key Bank [Member] Minimum [Member]	Dec. 31, 2013 Term Loan Facility from Key Bank [Member] Maximum [Member]	Sep. 30, 2014 Convertible Debt [Member]	Sep. 30, 2013 Convertible Debt [Member]	Sep. 30, 2014 Interest Rate Contract [Member]	Sep. 30, 2014 Interest Rate Swap [Member]
Debt Instrument [Line Items]
Mortgages and notes payable	$ 1,005,205,000			$ 1,197,489,000
Effective interest rate								8.10%		8.10%					2.20%	3.60%	8.50%	8.50%			1.15%				1.75%			1.35%
Weighted average interest rate	5.20%			5.30%
Face amount of debt instrument					500,000,000		255,000,000	24,786,000	115,000,000	28,991,000									250,000,000	250,000,000		400,000,000							250,000,000
Stated interest rate								6.00%		6.00%	6.00%	4.25%							4.40%
Percentage of issuance price																			99.883%	99.026%
Unamortized discount (premium)								966,000		1,500,000
Basis spread on variable rate																							0.95%	1.725%		1.50%	2.25%			1.10%	2.10%
Average variable interest rate																																			1.42%
Credit facility borrowings	0			48,000,000																		0
Amount of letters of credit outstanding						16,144,000
Remaining borrowing capacity on line of credit facility						383,856,000
Term of debt instrument																													5 years
Fixed interest rate																																		1.09%
Gross amount of long-term debt																																		250,000,000
Maturity date									Jan. 31, 2030
Percent of notes required to be repurchased at the option of the holders			100.00%
Conversion ratio numerator								149.6190
Conversion ratio denominator								1,000
Conversion price (dollars per share)								$ 6.68
Amount of debt converted																																4,205,000	54,905,000
Converted debt, shares issued	624,103	7,944,673
Convertible debt cash payments	62,000	3,270,000
Debt satisfaction charges	933,000	13,536,000
Gain (loss) on extinguishment of debt													$ 7,013,000	$ 11,860,000