Operating Leases - Lessor (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) ft² employees	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Operating Leases, Future Minimum Payments Receivable [Abstract]
2017	$ 734,157
2018	669,345
2019	589,515
2020	505,592
2021	412,924
Thereafter	1,643,594
Total	$ 4,555,127
Operating Leased Assets [Line Items]
Customer Concentration Risk - Number | employees	0
Concentration Risk, Percentage	18.00%
Ground Lease Expiration Date	2101
Office Lease Expiration Date	2029
Operating leases expenses	$ 18,400,000	$ 13,100,000	$ 9,500,000
Minimum [Member]
Operating Leased Assets [Line Items]
Operating leases, lease year range	3 years
Operating leases, lease year range for tenant space greater than 10,000 sq ft	5 years
Maximum [Member]
Operating Leased Assets [Line Items]
Operating leases, lease year range	7 years
Concentration Risk, Percentage	5.00%
Leases less than 10,000 sqft [Member]
Operating Leased Assets [Line Items]
Operating leases, tenant space terms | ft²	10,000
Leases greater then 10,000sqft [Member]
Operating Leased Assets [Line Items]
Operating leases, tenant space terms | ft²	10,000