Interest and Other Income, net - Schedule Of Interest And Other (Loss) Income, net (Parenthetical) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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	$ 223	$ 232	$ 442	$ 576
Preferred equity ownership percentage	24.40%		24.40%