Notes Payable - Additional Information (Detail) (USD $)											9 Months Ended		9 Months Ended								3 Months Ended		9 Months Ended			9 Months Ended				3 Months Ended						9 Months Ended		9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Interest Rate Forward Swap [Member] 2023 Notes [Member] Contract	Oct. 16, 2013 Interest Rate Forward Swap [Member] 2023 Notes [Member]	Sep. 30, 2014 Interest Rate Forward Swap [Member] 2024 Notes [Member] Contract	Jun. 10, 2014 Interest Rate Forward Swap [Member] 2024 Notes [Member]	Sep. 30, 2014 Secured Debt [Member]	Sep. 30, 2014 Secured Debt [Member] Fixed Rate Debt	Sep. 30, 2014 Unsecured Debt [Member]	Sep. 30, 2014 Unsecured Debt [Member] Senior Notes	Sep. 30, 2014 Unsecured Debt [Member] Senior Notes 2023 Notes [Member]	Oct. 16, 2013 Unsecured Debt [Member] Senior Notes 2023 Notes [Member]	Sep. 30, 2014 Unsecured Debt [Member] Senior Notes 2024 Notes [Member]	Jun. 10, 2014 Unsecured Debt [Member] Senior Notes 2024 Notes [Member]	Sep. 30, 2014 Unsecured Debt [Member] $500 million unsecured revolving credit faciltiy [Member]	Aug. 07, 2013 Unsecured Debt [Member] $500 million unsecured revolving credit faciltiy [Member]	Sep. 30, 2014 Individual property mortgages Secured Debt [Member] Fixed Rate Debt	Dec. 13, 2013 Colonial [Member] Unsecured Debt [Member] 6.25% Senior Notes due 2014 [Member]	Dec. 13, 2013 Colonial [Member] Unsecured Debt [Member] 5.5% Senior Notes due 2015 [Member]	Dec. 13, 2013 Colonial [Member] Unsecured Debt [Member] 6.05% Senior Notes due 2016 [Member]	Sep. 30, 2014 Limited Partner [Member]	Sep. 30, 2013 Limited Partner [Member]	Sep. 30, 2014 Limited Partner [Member]	Sep. 30, 2013 Limited Partner [Member]	Dec. 13, 2013 Limited Partner [Member]	Sep. 30, 2014 Limited Partner [Member] Unsecured Debt [Member] Exchange Notes [Member]	Dec. 13, 2013 Limited Partner [Member] Unsecured Debt [Member] 6.25% Senior Notes due 2014 [Member]	Dec. 13, 2013 Limited Partner [Member] Unsecured Debt [Member] 5.5% Senior Notes due 2015 [Member]	Dec. 13, 2013 Limited Partner [Member] Unsecured Debt [Member] 6.05% Senior Notes due 2016 [Member]	Sep. 30, 2014 Greenbrook [Member]	Sep. 30, 2014 Greenbrook [Member] Individual property mortgages Secured Debt [Member] Fixed Rate Debt	Sep. 30, 2014 Designated as Hedging Instrument [Member] Interest Rate Swap [Member] Contract	Sep. 30, 2014 Designated as Hedging Instrument [Member] Interest Rate Caps Contract	Sep. 30, 2014 Not Designated as Hedging Instrument [Member] Interest Rate Caps Contract	Sep. 30, 2014 Minimum [Member] Unsecured Debt [Member] Senior Notes	Sep. 30, 2014 Minimum [Member] Unsecured Debt [Member] $500 million unsecured revolving credit faciltiy [Member]	Sep. 30, 2014 Maximum [Member] Unsecured Debt [Member] Senior Notes	Sep. 30, 2014 Maximum [Member] Unsecured Debt [Member] $500 million unsecured revolving credit faciltiy [Member]
Debt Instrument [Line Items]
Notes Payable	$ 3,430,014,000	$ 3,470,000,000					$ 1,554,592,000	$ 1,215,496,000	$ 1,875,422,000								$ 1,090,496,000														$ 27,500,000
Debt Instrument, Face Amount												350,000,000		400,000,000		500,000,000
Debt Instrument, Basis Spread on Variable Rate																																				0.90%		1.70%
Debt Instrument, Interest Rate at Period End															1.10%
Line of Credit Facility, Amount Outstanding	0
Debt Instrument, Interest Rate, Stated Percentage												4.30%		3.75%				6.25%	5.50%	6.05%							6.25%	5.50%	6.05%
Debt Instrument, Issue Price												0.99047		0.98873
Debt Instrument, Unamortized Discount												3,300,000		4,500,000
Investment Banking, Advisory, Brokerage, and Underwriting Fees and Commissions											2,300,000		2,600,000
Proceeds from Notes Payable											344,400,000		392,900,000
Number of Interest Rate Derivatives Held			3		5
Derivative, Notional Amount			150,000,000		250,000,000																											625,000,000	165,000,000	90,326,031
Debt Instrument, Interest Rate, Effective Percentage	3.70%			4.15%		3.98%	3.40%	4.10%	4.00%								4.00%
Aggregate Principal Amount of Notes Exchanged																		154,200,000	169,200,000	68,100,000							154,200,000	169,100,000	68,100,000
Cash Received from Notes Exchange																									975,000
Debt Instrument, Interest Rate, Additional Interest, Maximum																										0.50%
Exchange Period																										270 days
Covenant Obligation, Debt to Total Asset Value										60.00%
Covenant Obligation, Secured Debt to Total Asset Value Ratio										40.00%
Covenant Obligation, Fixed Charge Ratio																																			150.00%		100.00%
Covenant Obligation, Unencumbered Leverage Ratio										150.00%
Loss on debt extinguishment/modification																					$ (2,586,000)	$ (218,000)	$ (2,586,000)	$ (387,000)						$ 2,600,000
Derivative, Number of Instruments Held																																9	6	14