Exchangeable Senior Notes - Schedule of Information about Total Carrying Amounts of Equity Components, Principal Amounts of Liability Components, Unamortized Discounts and Net Carrying Amounts for Notes (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Apr. 30, 2016	Feb. 29, 2016	Sep. 30, 2015	Jun. 21, 2013
Debt Instrument [Line Items]
Principal amount of liability components	$ 614,173	$ 610,314
Operating Partnership [Member]
Debt Instrument [Line Items]
Carrying amount of equity components	22,597	22,597
Unamortized debt issuance costs	(7,827)	(9,033)
Net carrying amount of liability components	614,173	610,314
Operating Partnership [Member] | Exchangeable Senior Notes 2.375% due 2033 (the 2013 Notes) [Member]
Debt Instrument [Line Items]
Carrying amount of equity components	0	0
Principal amount of liability components	63,170	63,170	$ 2,555	$ 19,639
Unamortized discount - equity components	(797)	(1,187)
Unamortized cash discount - 2013 Notes	(187)	(281)	(72)	(716)		$ (3,750)
Unamortized debt issuance costs			$ (7)	$ (36)		$ (1,672)
Operating Partnership [Member] | Exchangeable Senior Notes 3.125% due 2035 (the 2015 Notes) [Member]
Debt Instrument [Line Items]
Carrying amount of equity components	22,597	22,597
Principal amount of liability components	575,000	575,000
Unamortized discount - equity components	$ (15,186)	$ (17,355)
Unamortized debt issuance costs					$ (11,992)