2016 Acquisitions (Details) 2 $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Land and improvements	$ 65,105
Buildings and improvements	1,324,234
Acquired lease intangibles	200,185
Other assets	99,777
Total assets acquired	1,689,301
Notes payable and other debt	47,641
Intangible liabilities	103,769
Other liabilities	65,172
Total liabilities assumed	216,582
Noncontrolling interest assumed	24,656
Net assets acquired	1,448,063
Cash acquired	19,119
Total cash used	1,428,944
Triple Net Leased Properties
Business Acquisition [Line Items]
Land and improvements	1,579
Buildings and improvements	12,558
Acquired lease intangibles	163
Other assets	0
Total assets acquired	14,300
Notes payable and other debt	0
Intangible liabilities	0
Other liabilities	380
Total liabilities assumed	380
Noncontrolling interest assumed	0
Net assets acquired	13,920
Cash acquired	0
Total cash used	13,920
Office Operations
Business Acquisition [Line Items]
Land and improvements	63,526
Buildings and improvements	1,311,676
Acquired lease intangibles	200,022
Other assets	99,777
Total assets acquired	1,675,001
Notes payable and other debt	47,641
Intangible liabilities	103,769
Other liabilities	64,792
Total liabilities assumed	216,202
Noncontrolling interest assumed	24,656
Net assets acquired	1,434,143
Cash acquired	19,119
Total cash used	$ 1,415,024