SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ in Thousands	3 Months Ended										9 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019
Error Corrections and Prior Period Adjustments Restatement [Line Items]
CMBS rated below AA												3.10%
Fees And Other Income												$ 2,500
Increase in tenant real estate tax recoveries on net lease property				$ 1,100
Reduction in depreciation and amortization												(41,959)	$ (40,332)	$ (39,447)
Income tax expense (benefit)	$ 964	$ 1,204	$ 573	$ 3,902	$ 3,057	$ (576)	$ 6,606	$ (1,375)				6,643	7,712	6,320
Distributions from operations of investment in unconsolidated joint ventures												1,250	0	$ 1,017
Out-of-Period Adjustment Related to Prior Years
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Reduction in depreciation and amortization								$ (800)	$ (1,200)		$ (600)
Deferred financing cost amortization										$ 500
Tax Year 2015 [Member] | State and Local Jurisdiction
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Income tax expense (benefit)										1,200
Senior Unsecured Notes
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Debt Issuance Costs, Net	11,210											11,210
Senior Unsecured Notes | Various Date
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Debt Issuance Costs, Net	$ 11,200				$ 14,100							$ 11,200	$ 14,100
Consolidated Joint Ventures | Out-of-Period Adjustment Related to Prior Years
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Distributions from operations of investment in unconsolidated joint ventures										$ 900
Building | Minimum
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Property, Plant and Equipment, Useful Life												20 years
Building | Maximum
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Property, Plant and Equipment, Useful Life												47 years
Building Improvements | Minimum
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Property, Plant and Equipment, Useful Life												4 years
Building Improvements | Maximum
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Property, Plant and Equipment, Useful Life												15 years
Accounting Standards Update 2016-02 | Scenario, Forecast
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Finance Lease, Right-of-Use Asset															$ 3,700
Finance Lease, Liability, Noncurrent															$ 3,500