Future Minimum Lease Payments - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Siemens Real Estate [Member]
Future Minimum Leases Payments Under Leases [Line Items]
Total contribution of base rental	37.10%	24.70%
AT&T [Member]
Future Minimum Leases Payments Under Leases [Line Items]
Total contribution of base rental	14.80%