Supplemental Disclosure of Statement of Cash Flow Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Interest paid	$ 55,033	$ 50,691
Income taxes paid, net	1,444	1,687
2 of 21 Transferred Properties [Member] | NNN Office Joint Venture [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Transfer mortgage payable	103,400
LCIF [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Interest paid	14,775	11,527
Income taxes paid, net	68	$ 121
LCIF [Member] | 2 of 21 Transferred Properties [Member] | NNN Office Joint Venture [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Transfer mortgage payable	$ 45,900