SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	$ 416,300
Initial Cost
Land	221,785
Building and Improvements	881,838
Net Improvements (Write-Offs) Since Acquisition	125,157
Gross Amount at Which Carried
Land	221,785
Building and Improvements	1,006,995
Investments in real estate	1,228,780	$ 2,021,494
Accumulated Depreciation	271,055	$ 414,552	$ 369,661	$ 320,857
Other disclosures
Federal tax cost basis (unaudited)	1,233,414
Office | 260 Townsend San Francisco, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	28,200
Initial Cost
Land	7,574
Building and Improvements	13,843
Net Improvements (Write-Offs) Since Acquisition	3,333
Gross Amount at Which Carried
Land	7,574
Building and Improvements	17,176
Investments in real estate	24,750
Accumulated Depreciation	7,042
Office | 830 1st Street Washington, DC
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	46,000
Initial Cost
Land	18,095
Building and Improvements	62,017
Net Improvements (Write-Offs) Since Acquisition	(1,104)
Gross Amount at Which Carried
Land	18,095
Building and Improvements	60,913
Investments in real estate	79,008
Accumulated Depreciation	17,712
Office | 3601 S Congress Avenue Austin, TX
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	0
Initial Cost
Land	9,569
Building and Improvements	18,593
Net Improvements (Write-Offs) Since Acquisition	2,281
Gross Amount at Which Carried
Land	9,569
Building and Improvements	20,874
Investments in real estate	30,443
Accumulated Depreciation	7,060
Office | 899 N Capitol Street Washington, DC
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	0
Initial Cost
Land	34,641
Building and Improvements	84,466
Net Improvements (Write-Offs) Since Acquisition	15,361
Gross Amount at Which Carried
Land	34,641
Building and Improvements	99,827
Investments in real estate	134,468
Accumulated Depreciation	28,822
Office | 999 N Capitol Street Washington, DC
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	0
Initial Cost
Land	32,221
Building and Improvements	86,526
Net Improvements (Write-Offs) Since Acquisition	13,615
Gross Amount at Which Carried
Land	32,221
Building and Improvements	100,141
Investments in real estate	132,362
Accumulated Depreciation	29,563
Office | 901 N Capitol Street Washington, DC
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	0
Initial Cost
Land	27,117
Building and Improvements	0
Net Improvements (Write-Offs) Since Acquisition	4,329
Gross Amount at Which Carried
Land	27,117
Building and Improvements	4,329
Investments in real estate	31,446
Accumulated Depreciation	1,349
Office | 1333 Broadway Oakland, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	39,500
Initial Cost
Land	7,048
Building and Improvements	41,578
Net Improvements (Write-Offs) Since Acquisition	9,386
Gross Amount at Which Carried
Land	7,048
Building and Improvements	50,964
Investments in real estate	58,012
Accumulated Depreciation	13,385
Office | 1901 Harrison Street Oakland, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	42,500
Initial Cost
Land	3,838
Building and Improvements	68,106
Net Improvements (Write-Offs) Since Acquisition	9,273
Gross Amount at Which Carried
Land	3,838
Building and Improvements	77,379
Investments in real estate	81,217
Accumulated Depreciation	22,176
Office | 2100 Franklin Street Oakland, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	80,000
Initial Cost
Land	4,277
Building and Improvements	34,033
Net Improvements (Write-Offs) Since Acquisition	10,506
Gross Amount at Which Carried
Land	4,277
Building and Improvements	44,539
Investments in real estate	48,816
Accumulated Depreciation	14,489
Office | 2101 Webster Street Oakland, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	83,000
Initial Cost
Land	4,752
Building and Improvements	109,812
Net Improvements (Write-Offs) Since Acquisition	32,394
Gross Amount at Which Carried
Land	4,752
Building and Improvements	142,206
Investments in real estate	146,958
Accumulated Depreciation	41,100
Office | 2353 Webster Street Parking Garage Oakland, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	0
Initial Cost
Land	0
Building and Improvements	9,138
Net Improvements (Write-Offs) Since Acquisition	29
Gross Amount at Which Carried
Land	0
Building and Improvements	9,167
Investments in real estate	9,167
Accumulated Depreciation	2,125
Office | 1 Kaiser Plaza Oakland, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	97,100
Initial Cost
Land	9,261
Building and Improvements	113,619
Net Improvements (Write-Offs) Since Acquisition	18,073
Gross Amount at Which Carried
Land	9,261
Building and Improvements	131,692
Investments in real estate	140,953
Accumulated Depreciation	35,942
Office | 2 Kaiser Plaza Parking Lot Oakland, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	0
Initial Cost
Land	10,931
Building and Improvements	110
Net Improvements (Write-Offs) Since Acquisition	1,504
Gross Amount at Which Carried
Land	10,931
Building and Improvements	1,614
Investments in real estate	12,545
Accumulated Depreciation	54
Office | 11600 Wilshire Blvd Los Angeles, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	0
Initial Cost
Land	3,477
Building and Improvements	18,522
Net Improvements (Write-Offs) Since Acquisition	1,969
Gross Amount at Which Carried
Land	3,477
Building and Improvements	20,491
Investments in real estate	23,968
Accumulated Depreciation	4,388
Office | 11620 Wilshire Blvd Los Angeles, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	0
Initial Cost
Land	7,672
Building and Improvements	51,999
Net Improvements (Write-Offs) Since Acquisition	7,949
Gross Amount at Which Carried
Land	7,672
Building and Improvements	59,948
Investments in real estate	67,620
Accumulated Depreciation	13,291
Office | 4750 Wilshire Blvd Los Angeles, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	0
Initial Cost
Land	16,633
Building and Improvements	28,985
Net Improvements (Write-Offs) Since Acquisition	58
Gross Amount at Which Carried
Land	16,633
Building and Improvements	29,043
Investments in real estate	45,676
Accumulated Depreciation	3,206
Office | Lindblade Media Center Los Angeles, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	0
Initial Cost
Land	6,342
Building and Improvements	11,568
Net Improvements (Write-Offs) Since Acquisition	0
Gross Amount at Which Carried
Land	6,342
Building and Improvements	11,568
Investments in real estate	17,910
Accumulated Depreciation	1,235
Office | 1130 Howard Street San Francisco, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	0
Initial Cost
Land	8,290
Building and Improvements	10,480
Net Improvements (Write-Offs) Since Acquisition	0
Gross Amount at Which Carried
Land	8,290
Building and Improvements	10,480
Investments in real estate	18,770
Accumulated Depreciation	0
Hotel | Sheraton Grand Hotel Sacramento, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	0
Initial Cost
Land	3,497
Building and Improvements	107,447
Net Improvements (Write-Offs) Since Acquisition	(3,688)
Gross Amount at Which Carried
Land	3,497
Building and Improvements	103,759
Investments in real estate	107,256
Accumulated Depreciation	25,449
Hotel | Sheraton Grand Hotel Parking & Retail Sacramento, CA
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	0
Initial Cost
Land	6,550
Building and Improvements	10,996
Net Improvements (Write-Offs) Since Acquisition	(111)
Gross Amount at Which Carried
Land	6,550
Building and Improvements	10,885
Investments in real estate	17,435
Accumulated Depreciation	$ 2,667