Fair Value Measurements - Financial Assets and Liabilities Not Measured at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Carrying Amount
Assets:
Cash equivalents	$ 259,774	$ 273,914
Rego Park II loan participation	197,018	198,537
Assets	456,792	472,451
Liabilities:
Mortgages payable (excluding deferred debt issuance costs, net)	1,172,234	1,252,440
Fair Value
Assets:
Assets	456,774	471,914
Fair Value | Level 1
Assets:
Cash equivalents	259,774	273,914
Fair Value | Level 2
Assets:
Rego Park II loan participation	197,000	198,000
Liabilities:
Mortgages payable (excluding deferred debt issuance costs, net)	$ 1,162,000	$ 1,239,000