Commitments and Contingencies - Narrative (Details)
3 Months Ended 12 Months Ended
Mar. 31, 2019
USD ($)
renewal_option
ground_lease
tenant
claim
Dec. 31, 2018
USD ($)
Commitments and Contingencies Disclosure [Abstract]    
Contingently liable amount of debt owed by tenant $ 5,700,000 $ 5,700,000
Number of tenants indemnified by | tenant 1  
Accruals made for environmental remediation $ 0  
Outstanding claims | claim 0  
Total commitments $ 49,100,000  
Total commitments relating to future acquisitions 14,600,000  
Commitments to purchase capital assets within one year expected to be funded within one year $ 39,800,000  
Operating lease number of renewal options | renewal_option 2  
Operating lease renewal term 5 years  
Number of long-term non-cancelable ground leases | ground_lease 4  
Operating lease, weighted average remaining lease term 8 years 3 months  
Operating lease, weighted average discount rate 4.30%  
Incentive to lessee $ 1,700,000  
Operating lease, right-of-use assets $ 6,100,000