Marketable Securities - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018	Dec. 31, 2017
Investment Holdings [Line Items]
Change in fair value of marketable securities (see Note 7)	$ 433	$ 0	$ (4,737)	$ 0
Macerich Interest
Investment Holdings [Line Items]
Macerich common shares	535,265		535,265			535,265
Economic basis per share	$ 56.05		$ 56.05
Economic cost	$ 30,000		$ 30,000
Fair value	$ 30,419		$ 30,419			$ 35,156
Closing share price	$ 56.83		$ 56.83		$ 56.02	$ 65.68
Change in fair value of marketable securities (see Note 7)			$ (4,737)