Interest and Other Income (Loss), net - Schedule Of Interest And Other Income (Loss), net (Parenthetical) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Preferred equity ownership percentage	24.40%		24.40%
PGRESS Equity Holdings L.P. [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Preferred equity investment income, attributable to parent	$ 227	$ 243	$ 669	$ 819
Preferred equity ownership percentage	24.40%		24.40%
PGRESS Equity Holdings L.P. [Member] | 2 Herald Square [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Preferred equity ownership percentage		24.40%		24.40%
Valuation allowance on preferred equity investment, attributable to parent		$ 4,780		$ 4,780
Valuation allowance on preferred equity investment attributable to noncontrolling interests		$ 14,808		$ 14,808