Notes and Bonds Payable - Narrative (Details) (USD $)	3 Months Ended	12 Months Ended				1 Months Ended	0 Months Ended			0 Months Ended		12 Months Ended				12 Months Ended		12 Months Ended				0 Months Ended			12 Months Ended	1 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011	Feb. 15, 2013 Unsecured Credit Facility due 2015 [Member] Line of Credit [Member]	Feb. 15, 2013 Line of Credit [Member] Unsecured Credit Facility due 2015 [Member] extension_option	Dec. 31, 2013 Line of Credit [Member] Unsecured Credit Facility due 2015 [Member]	Oct. 14, 2011 Line of Credit [Member] Unsecured Credit Facility due 2015 [Member] Lender	Feb. 15, 2013 Line of Credit [Member] Unsecured Credit Facility due 2015 [Member] Minimum [Member]	Feb. 15, 2013 Line of Credit [Member] Unsecured Credit Facility due 2015 [Member] Maximum [Member]	Dec. 31, 2013 Senior Notes [Member] 5.750% Senior Notes Due 2021 [Member]	Dec. 31, 2012 Senior Notes [Member] 5.750% Senior Notes Due 2021 [Member]	Dec. 31, 2011 Senior Notes [Member] 5.750% Senior Notes Due 2021 [Member]	Dec. 13, 2010 Senior Notes [Member] 5.750% Senior Notes Due 2021 [Member]	Dec. 31, 2013 Senior Notes [Member] 3.75% Senior Notes Due 2023 [Member]	Mar. 26, 2013 Senior Notes [Member] 3.75% Senior Notes Due 2023 [Member]	Dec. 31, 2013 Senior Notes [Member] 6.500% Senior Notes Due 2017 [Member]	Dec. 31, 2012 Senior Notes [Member] 6.500% Senior Notes Due 2017 [Member]	Dec. 31, 2011 Senior Notes [Member] 6.500% Senior Notes Due 2017 [Member]	Dec. 04, 2009 Senior Notes [Member] 6.500% Senior Notes Due 2017 [Member]	Apr. 18, 2013 Senior Notes [Member] 5.125% Senior Notes Due 2014 [Member]	Dec. 31, 2013 Senior Notes [Member] 5.125% Senior Notes Due 2014 [Member]	Dec. 31, 2012 Senior Notes [Member] 5.125% Senior Notes Due 2014 [Member]	Dec. 31, 2013 Mortgage notes payable [Member]	Jun. 30, 2013 Mortgage notes payable [Member] Mortgage Notes Seven Point Two Five Zero Percent [Member]	Dec. 31, 2013 Mortgage notes payable [Member] 5.000%-7.625% Mortgage Notes Payable [Member]	Dec. 31, 2012 Mortgage notes payable [Member] 5.000%-7.625% Mortgage Notes Payable [Member]	Dec. 31, 2011 Mortgage notes payable [Member] 5.000%-7.625% Mortgage Notes Payable [Member]
Debt Instrument [Line Items]
Unsecured credit facility									$ 700,000,000.0
Number of Lenders of unsecured credit facility									17
Number of extension options							2
Period of extension option							6 months
Extension fees as percentage of aggregate commitments							0.075%
Percentage of interest in addition to LIBOR							1.40%			0.95%	1.75%
Facility fee on the aggregate amount of commitments							0.30%			0.15%	0.35%
Deferred finance costs, gross											2,700,000
Anticipated write off of unamortized deferred financing costs						300,000
Amount outstanding under Unsecured Credit Facility								238,000,000
Weighted average interest rate (LOC)								1.57%
Remaining borrowing capacity								462,000,000
Redemption of unsecured senior notes		19,984,000		4,990,000	3,703,000																	277,300,000				94,300,000
Outstanding principal of unsecured senior notes																						264,700,000				77,000,000
Senior notes face value												400,000,000	400,000,000		400,000,000	250,000,000	250,000,000	300,000,000	300,000,000		300,000,000		0	264,737,000			166,684,000	225,242,000
Interest rate on senior notes												5.75%			5.75%	3.75%	3.75%	6.50%			6.50%	5.125%	5.125%			7.25%
Unaccreted discount												2,422,000	2,693,000			1,923,000	2,100,000	992,000	1,272,000				0	215,000			888,000	2,755,000
Unamortized discount (premium)		6,225,000	[1]												3,200,000						2,000,000	200,000
Extinguishment of Debt, Accrued Interest Amount																						700,000				500,000
Make Whole Interest on Extinguishment Of Debt																						11,900,000				16,800,000
Write off of Deferred Debt Issuance Cost																						200,000				500,000
Gains (Losses) on Extinguishment of Debt	(29,900,000)	(29,638,000)			(1,986,000)																	12,300,000				17,400,000
Authorized Repurchase Of Debt Amount																		50,000,000
Interest rate yielded per annum upon issuance															5.855%		3.849%				6.618%
Amount of amortization included in interest expense on the Company's consolidated Statements of operations												$ 300,000	$ 300,000	$ 0		$ 100,000		$ 300,000	$ 300,000	$ 200,000							$ 400,000	$ 300,000	$ 700,000
Debt Instrument principal and interest amortization period																									15 years

[1] Includes discount accretion and premium amortization related to the Company’s Senior Notes due 2017, Senior Notes due 2021, Senior Notes due 2023, and fifteen mortgage notes payable.