Credit Facilities and Mortgage Notes Payable - Unsecured Credit Facility - Additional Information (Detail) (USD $) In Millions, unless otherwise specified		6 Months Ended			1 Months Ended					1 Months Ended		6 Months Ended		0 Months Ended	1 Months Ended
	Jun. 30, 2014	Jun. 30, 2014 Term Loan [Member]	Jun. 30, 2014 Revolving Credit Facility [Member]	Jun. 30, 2014 Letter of Credit [Member]	Aug. 31, 2014 Subsequent Event [Member] Unsecured Credit Facility [Member]	Jun. 30, 2014 Minimum [Member] Libor Rate [Member]	Jun. 30, 2014 Minimum [Member] Base Rate [Member]	Jun. 30, 2014 Maximum [Member] Libor Rate [Member]	Jun. 30, 2014 Maximum [Member] Base Rate [Member]	Apr. 30, 2014 Unsecured Credit Facility [Member]	Feb. 28, 2014 Unsecured Credit Facility [Member]	Jun. 30, 2014 Unsecured Credit Facility [Member]	Jun. 30, 2014 Unsecured Credit Facility [Member] Term Loan [Member]	Jul. 23, 2014 Unsecured Credit Facility [Member] Subsequent Event [Member]	Apr. 30, 2014 Unsecured Credit Facility [Member] Maximum [Member]
Debt Instrument [Line Items]
Credit facility agreement date												May 01, 2013
Credit Facility maximum borrowing capacity		$ 225	$ 350								$ 400	$ 575
Unsecured Credit Facility term		5 years	4 years
Increase the amount of line of credit facility												675
Unsecured revolving credit facility											50
Amount of unsecured revolving credit facility expanded					10
Current revolving Credit facility					410
Additional letter of credit outstanding				3
Leverage Ratio						2.10%	1.10%	2.85%	1.85%
Line of credit facility weighted average interest rate outstanding percentage	2.25%
Repayment of unsecured debt										225					150
Repayment of term loan													$ 75
Interest rate of senior note												5.875%		5.875%