Mortgage and Other Indebtedness (Details)	3 Months Ended
	Mar. 31, 2016 USD ($) loan derivative_instrument extension_option credit_line	Dec. 31, 2015 USD ($) loan derivative_instrument	Dec. 31, 2014 USD ($)	Oct. 31, 2014	Dec. 31, 2013 USD ($)	Nov. 30, 2013
Debt Instrument [Line Items]
Weighted Average Interest Rate (percent)	4.56%	4.54%
Long-term debt, percentage bearing fixed interest, amount	$ 3,466,259,000	$ 3,485,308,000
Mortgage and other indebtedness amount carrying value	1,232,515,000	1,241,379,000
Total fixed-rate and variable-rate debt	4,698,774,000	4,726,687,000
Unamortized deferred financing costs	(15,287,000)	(16,059,000)
Total mortgage and other indebtedness	$ 4,683,487,000	$ 4,710,628,000
Wells Fargo Bank
Debt Instrument [Line Items]
Line of credit, extension fee (percent)	0.15%
Fixed Rate Interest
Debt Instrument [Line Items]
Weighted Average Interest Rate (percent)	5.53%	5.53%
Variable Rate Interest Member
Debt Instrument [Line Items]
Weighted Average Interest Rate (percent)	1.84%	1.76%
Interest Rate Swap
Debt Instrument [Line Items]
Number of unsecured term loans | loan		4
Derivative, Number of Instruments Held | derivative_instrument	4	4
Derivative, Notional Amount	$ 100,009,000	$ 101,151,000
Unsecured lines of credit
Debt Instrument [Line Items]
Number of unsecured term loans | credit_line	3
Mortgage and other indebtedness amount carrying value	$ 387,186,000
Loan agreement, basis spread on variable rate (as a percentage)	1.20%
Annual facility Fee (percent)	0.25%
Total Capacity	$ 1,100,000,000
Unsecured lines of credit | Minimum
Debt Instrument [Line Items]
Loan agreement, basis spread on variable rate (as a percentage)	0.875%
Annual facility Fee (percent)	0.125%
Unsecured lines of credit | Maximum
Debt Instrument [Line Items]
Loan agreement, basis spread on variable rate (as a percentage)	1.55%
Annual facility Fee (percent)	0.30%
Unsecured term loans
Debt Instrument [Line Items]
Debt instrument, face amount	$ 400,000,000
Loan agreement, basis spread on variable rate (as a percentage)	1.50%
Interest rate at period end (as a percent)	1.94%
Wells Fargo - Facility A
Debt Instrument [Line Items]
Mortgage and other indebtedness amount carrying value	$ 0
Total Capacity	500,000,000
First Tennessee
Debt Instrument [Line Items]
Mortgage and other indebtedness amount carrying value	27,800,000
Total Capacity	$ 100,000,000
First Tennessee | Wells Fargo Bank
Debt Instrument [Line Items]
Line of credit, extension fee (percent)	0.20%
Wells Fargo - Facility B
Debt Instrument [Line Items]
Mortgage and other indebtedness amount carrying value	$ 359,386,000
Total Capacity	500,000,000
Wells Fargo Bank
Debt Instrument [Line Items]
Total Capacity	30,000,000
Letter of credit, outstanding	5,464,000
First Tennessee Bank
Debt Instrument [Line Items]
Total Capacity	20,000,000
Letter of credit, outstanding	113,000
Unsecured Term Loan 2
Debt Instrument [Line Items]
Debt instrument, face amount	$ 350,000,000
Loan agreement, basis spread on variable rate (as a percentage)	1.35%
Number of extension options available | extension_option	2
Debt instrument, option extension term (in years)	1 year
Interest rate at period end (as a percent)	1.78%
Unsecured Term Loan 3
Debt Instrument [Line Items]
Weighted Average Interest Rate (percent)	1.99%
Debt instrument, face amount	$ 50,000,000
Loan agreement, basis spread on variable rate (as a percentage)	1.55%
Senior Unsecured Notes
Debt Instrument [Line Items]
Debt instrument, face amount					$ 450,000,000
Notice required to redeem debt, term	30 days
Debt instrument, redemption price, percentage	100.00%
Senior Unsecured Notes | Minimum
Debt Instrument [Line Items]
Secured debt to total assets (as a percent)	40.00%
Senior Unsecured Notes | Fixed Rate Interest
Debt Instrument [Line Items]
Weighted Average Interest Rate (percent)					5.25%	5.25%
Senior Unsecured Notes | Fixed Rate Interest | Minimum
Debt Instrument [Line Items]
Debt instrument, increase in variable interest rate	0.25%
Senior Unsecured Notes | Fixed Rate Interest | Maximum
Debt Instrument [Line Items]
Debt instrument, increase in variable interest rate	1.00%
Senior Unsecured Notes | Fixed Rate Operating Loans
Debt Instrument [Line Items]
Unamortized debt discount	$ 3,751,000	3,849,000
Senior Unsecured Notes | Required
Debt Instrument [Line Items]
Secured debt to total assets (as a percent)	45.00%
Total debt to total asset value (as a percent)	60.00%
Total Unencumbered Assets to Unsecured Debt (as a percent)	150.00%
Consolidated income available for debt service to annual debt service charge (as a percent)	150.00%
Senior Unsecured Notes | Actual
Debt Instrument [Line Items]
Secured debt to total assets (as a percent)	31.00%
Total debt to total asset value (as a percent)	54.00%
Total Unencumbered Assets to Unsecured Debt (as a percent)	218.00%
Consolidated income available for debt service to annual debt service charge (as a percent)	320.00%
Non-recourse loans on operating properties
Debt Instrument [Line Items]
Long-term debt, percentage bearing fixed interest, amount	$ 2,720,015,000	2,736,538,000
Mortgage and other indebtedness amount carrying value	19,355,000	$ 16,840,000
Debt instrument, debt default threshold, minimum loan amount	$ 50,000,000
Non-recourse loans on operating properties | Fixed Rate Interest
Debt Instrument [Line Items]
Weighted Average Interest Rate (percent)	5.68%	5.68%
Non-recourse loans on operating properties | Variable Rate Interest Member
Debt Instrument [Line Items]
Weighted Average Interest Rate (percent)	2.87%	2.49%
Senior Notes Due 2023
Debt Instrument [Line Items]
Long-term debt, percentage bearing fixed interest, amount	$ 446,249,000	$ 446,151,000
Debt instrument, redemption price, percentage	100.00%
Senior Notes Due 2023 | Minimum
Debt Instrument [Line Items]
Secured debt to total assets (as a percent)	40.00%
Senior Notes Due 2023 | Maximum
Debt Instrument [Line Items]
Secured debt to total assets (as a percent)	45.00%
Senior Notes Due 2023 | Fixed Rate Interest
Debt Instrument [Line Items]
Weighted Average Interest Rate (percent)	5.25%	5.25%
Senior Notes Due 2023 | Treasury Rate
Debt Instrument [Line Items]
Derivative, basis spread on variable rate	0.40%
Senior Notes Due 2024
Debt Instrument [Line Items]
Long-term debt, percentage bearing fixed interest, amount	$ 299,934,000	$ 299,933,000
Debt instrument, redemption price, percentage	100.00%
Senior Notes Due 2024 | Fixed Rate Interest
Debt Instrument [Line Items]
Weighted Average Interest Rate (percent)	4.60%	4.60%	4.60%	4.60%
Senior Notes Due 2024 | Treasury Rate
Debt Instrument [Line Items]
Derivative, basis spread on variable rate	0.35%
Other
Debt Instrument [Line Items]
Long-term debt, percentage bearing fixed interest, amount	$ 61,000	$ 2,686,000
Other | Fixed Rate Interest
Debt Instrument [Line Items]
Weighted Average Interest Rate (percent)	3.50%	3.50%
Recourse term loans on operating properties
Debt Instrument [Line Items]
Mortgage and other indebtedness amount carrying value	$ 25,974,000	$ 25,635,000
Debt instrument, debt default threshold, minimum loan amount	$ 150,000,000
Recourse term loans on operating properties | Variable Rate Interest Member
Debt Instrument [Line Items]
Weighted Average Interest Rate (percent)	3.03%	2.97%
Unsecured lines of credit
Debt Instrument [Line Items]
Mortgage and other indebtedness amount carrying value	$ 387,186,000	$ 398,904,000
Unsecured lines of credit | Variable Rate Interest Member
Debt Instrument [Line Items]
Weighted Average Interest Rate (percent)	1.63%	1.54%
Unsecured term loans
Debt Instrument [Line Items]
Mortgage and other indebtedness amount carrying value	$ 800,000,000	$ 800,000,000
Unsecured term loans | Variable Rate Interest Member
Debt Instrument [Line Items]
Weighted Average Interest Rate (percent)	1.87%	1.82%
Unsecured lines of credit
Debt Instrument [Line Items]
Number of unsecured term loans | loan	3
Unsecured lines of credit | Senior Notes Due 2024
Debt Instrument [Line Items]
Unamortized debt discount	$ 66,000	$ 67,000
Debt instrument, face amount			$ 300,000,000
Wells Fargo Bank
Debt Instrument [Line Items]
Letter of credit, outstanding	$ 350,000
Unsecured Credit Facility and Term Loan | Required
Debt Instrument [Line Items]
Total debt to total asset value (as a percent)	60.00%
Total Unencumbered Assets to Unsecured Debt (as a percent)	160.00%
Unencumbered NOI to unsecured interest expense (as a percent)	175.00%
EBITDA to fixed charges (debt service) (as a percent)	150.00%
Unsecured Credit Facility and Term Loan | Actual
Debt Instrument [Line Items]
Total debt to total asset value (as a percent)	50.00%
Total Unencumbered Assets to Unsecured Debt (as a percent)	230.00%
Unencumbered NOI to unsecured interest expense (as a percent)	490.00%
EBITDA to fixed charges (debt service) (as a percent)	230.00%