Investments - Operating Lease Income (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Lessor, Lease, Description [Line Items]        
Base cash rent $ 98,418   $ 195,217  
Variable cash rent (including reimbursables) 2,942   6,580  
Straight-line rent, net of bad debt expense 4,485   7,392  
Amortization of above- and below- market lease intangibles, net 661   1,384  
Total rental income 106,506   210,573  
In-place leases        
Lessor, Lease, Description [Line Items]        
Leases amortization expenses $ 6,500 $ 8,700 $ 13,200 $ 18,700
Continuing and discontinuing operations        
Lessor, Lease, Description [Line Items]        
Base cash rent   129,388   279,835
Variable cash rent (including reimbursables)   3,591   9,121
Straight-line rent, net of bad debt expense   4,187   9,087
Amortization of above- and below- market lease intangibles, net   1,219   2,372
Total rental income   $ 138,385   $ 300,415