Commitments and contingencies Future Minimum Lease Obligations Schedule (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Office Leases
2016	$ 1,554
2017	1,623
2018	1,700
2019	1,633
2020	178
Thereafter	339
Total	7,027
Ground Leases
2016	12,660
2017	12,614
2018	12,828
2019	11,313
2020	11,414
Thereafter	613,156
Total	673,985
Total
2016	14,214
2017	14,237
2018	14,528
2019	12,946
2020	11,592
Thereafter	613,495
Total	$ 681,012