Investment in Office Properties - Contractual Obligations and Minimum Rental Receipts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Contractual Obligations and Minimum Rental Receipts [Abstract]
2016	$ 56,708
2017	2,377
2018	10
2019	114
2020	3,007
Thereafter	25
Total	62,241
Minimum future operating lease payments
2016	163
2017	122
2018	72
2019	9
2020	0
Total	366
Future approximate minimum rental receipts under noncancelable leases [Abstract]
2016	358,388
2017	361,162
2018	332,595
2019	297,855
2020	267,131
Thereafter	1,119,145
Total	2,736,276
Property Subject to or Available for Operating Lease [Line Items]
2016	358,388
2017	361,162
2018	332,595
2019	297,855
2020	267,131
Thereafter	1,119,145
Total	2,736,276
Ground rent expenses	$ 1,500	$ 601	$ 198
Corporate Center I, II, and III
Property Subject to or Available for Operating Lease [Line Items]
Ground lease remaining term	65 years
Ground lease payment adjustment percentage	5.00%
Corporate Center IV
Property Subject to or Available for Operating Lease [Line Items]
Ground lease remaining term	65 years
NASCAR Plaza
Property Subject to or Available for Operating Lease [Line Items]
Remaining lease term	90 years
Corporate Center V
Property Subject to or Available for Operating Lease [Line Items]
Ground lease remaining term	65 years
Lincoln Place
Property Subject to or Available for Operating Lease [Line Items]
Remaining lease term	34 years
Land
Future approximate minimum rental receipts under noncancelable leases [Abstract]
2016	$ 1,264
2017	1,294
2018	1,294
2019	1,294
2020	1,296
Thereafter	91,378
Total	97,820
Property Subject to or Available for Operating Lease [Line Items]
2016	1,264
2017	1,294
2018	1,294
2019	1,294
2020	1,296
Thereafter	91,378
Total	$ 97,820