Real Estate - Schedule of Development in Process Activities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($) property
Property, Plant and Equipment [Line Items]
Number of properties under development | property	3	3
Real estate under development	$ 193,315	$ 120,297
Transfers In	69,655
Capitalized Costs	3,363
Transfers Out	$ 0
Core Portfolio
Property, Plant and Equipment [Line Items]
Number of properties under development | property	1	1
Real estate under development	$ 65,354	$ 7,759
Transfers In	57,342
Capitalized Costs	253
Transfers Out	$ 0
Fund Portfolio | Fund II
Property, Plant and Equipment [Line Items]
Number of properties under development | property	0	0
Real estate under development	$ 8,200	$ 7,462
Transfers In	0
Capitalized Costs	738
Transfers Out	$ 0
Fund Portfolio | Fund III
Property, Plant and Equipment [Line Items]
Number of properties under development | property	1	1
Real estate under development	$ 34,197	$ 21,242
Transfers In	12,313
Capitalized Costs	642
Transfers Out	$ 0
Fund Portfolio | Fund IV
Property, Plant and Equipment [Line Items]
Number of properties under development | property	1	1
Real estate under development	$ 85,564	$ 83,834
Transfers In	0
Capitalized Costs	1,730
Transfers Out	$ 0