Lines of Credit - Additional Information (Detail)		12 Months Ended
	Oct. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) Bank	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Line of Credit Facility [Line Items]
Line of credit facility		$ 690,000,000	$ 765,000,000
2013 Credit Facility [Member]
Line of Credit Facility [Line Items]
Expiration date of unsecured revolving line of credit		Nov. 15, 2018
Number of banks with which agreement made | Bank		12
Number of years for unsecured revolving line of credit		5 years
Line of credit facility		$ 400,000,000	400,000,000
Debt instrument basis spread on LIBOR minimum on a three day advance notice		1.25%
Debt instrument basis spread on LIBOR maximum on a three day advance notice		2.00%
Debt instrument basis spread on variable rate minimum on same day borrowing		0.25%
Debt instrument basis spread on variable rate maximum on same day borrowing		1.00%
Federal funds effective rate plus 1%		1.00%
LIBOR rate plus 1%		1.00%
Maximum leverage ratio required to be maintained by partnership		35.00%
Required minimum partnership capital, net of reserve for anticipated withdrawals		$ 1,382,000,000
Additional issuances of partnership capital		50.00%
Amount outstanding under credit facility		$ 0	0
Partnership draws against lines of credit		0	0	$ 0
Uncommitted Secured Credit Facilities [Member]
Line of Credit Facility [Line Items]
Line of credit facility		290,000,000	365,000,000
Decrease in credit facility	$ 75,000,000
Amount outstanding under credit facility		0	0
Partnership draws against lines of credit		$ 0	$ 0	$ 0