Fair Value Measurements - Financial Assets and Liabilities Not Measured at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Carrying Amount
Assets:
Cash equivalents	$ 259,556	$ 273,914
Rego Park II loan participation	197,784	198,537
Assets	457,340	472,451
Liabilities:
Mortgages payable (excluding deferred debt issuance costs, net)	1,251,469	1,252,440
Fair Value
Assets:
Assets	456,556	471,914
Fair Value | Level 1
Assets:
Cash equivalents	259,556	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)	$ 1,241,000	$ 1,239,000