Related Party and Affiliated Real Estate Joint Venture Transactions - Summarized Information of Management Fee Revenues for Related Party and Affiliated Joint Ventures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Management fee revenues and other income	$ 39,379	$ 39,842	$ 34,161
PRISA
Related Party Transaction [Line Items]
Management fee revenues and other income	6,303	6,117	5,809
SP I
Related Party Transaction [Line Items]
Management fee revenues and other income	1,450	1,397	1,312
WCOT
Related Party Transaction [Line Items]
Management fee revenues and other income	1,159	1,819	1,799
VRS
Related Party Transaction [Line Items]
Management fee revenues and other income	1,038	1,053	1,398
ESNPS
Related Party Transaction [Line Items]
Management fee revenues and other income	645	620	584
ESW
Related Party Transaction [Line Items]
Management fee revenues and other income	590	555	515
ESW II
Related Party Transaction [Line Items]
Management fee revenues and other income	502	482	452
PRISA II
Related Party Transaction [Line Items]
Management fee revenues and other income	0	3,469	4,703
Other
Related Party Transaction [Line Items]
Management fee revenues and other income	$ 27,692	$ 24,330	$ 17,589