Investments (Tables)
 12 Months Ended
Dec. 31, 2017
Investments in and Advances to Affiliates, Schedule of Investments [Abstract]  
Summary of Gross Real Estate and Loan Activity
During the years ended December 31, 2017 and 2016, the Company had the following real estate and loan activity, net of accumulated depreciation and amortization:
 
Number of Properties
 
Dollar Amount of Investments
 
Owned
 
Financed
 
Total
 
Owned
 
Financed
 
Total
 
 
 
 
 
 

 
(In Thousands)
Gross balance, December 31, 2015
2,485

 
144

 
2,629

 
$
8,198,685

 
$
104,003

 
$
8,302,688

Acquisitions/improvements (1)
269

 
—

 
269

 
711,510

 
—

 
711,510

Dispositions of real estate (2)(3)
(213
)
 
—

 
(213
)
 
(598,662
)
 
—

 
(598,662
)
Principal payments and payoffs
—

 
(70
)
 
(70
)
 
—

 
(34,955
)
 
(34,955
)
Impairments
—

 
—

 
—

 
(88,073
)
 
(176
)
 
(88,249
)
Write-off of gross lease intangibles
—

 
—

 
—

 
(42,307
)
 
—

 
(42,307
)
Loan premium amortization and other
—

 
—

 
—

 
(77
)
 
(2,294
)
 
(2,371
)
Gross balance, December 31, 2016
2,541

 
74

 
2,615

 
8,181,076

 
66,578

 
8,247,654

Acquisitions/improvements (1)
43

 
16

 
59

 
326,766

 
23,300

 
350,066

Dispositions of real estate (2)(3)
(192
)
 
—

 
(192
)
 
(510,863
)
 
—

 
(510,863
)
Principal payments and payoffs
—

 
(2
)
 
(2
)
 
—

 
(7,878
)
 
(7,878
)
Impairments
—

 
—

 
—

 
(101,941
)
 
(389
)
 
(102,330
)
Write-off of gross lease intangibles
—

 
—

 
—

 
(67,139
)
 
—

 
(67,139
)
Loan premium amortization and other
—

 
—

 
—

 
(4,841
)
 
(1,644
)
 
(6,485
)
Gross balance, December 31, 2017
2,392

 
88

 
2,480

 
$
7,823,058

 
$
79,967

 
$
7,903,025

Accumulated depreciation and amortization
 
 
 
 
 
 
(1,289,304
)
 
—

 
(1,289,304
)
Other
 
 
 
 
 
 
304

 
—

 
304

Net balance, December 31, 2017
 
 
 
 
 
 
$
6,534,058

 
$
79,967

 
$
6,614,025


(1) 
Includes investments of $42.6 million and $20.5 million, respectively, in revenue producing capitalized expenditures, as well as $3.5 million and $6.6 million, respectively, of non-revenue producing capitalized expenditures for the years ended December 31, 2017 and 2016.
(2) 
The total accumulated depreciation and amortization associated with dispositions of real estate was $57.1 million and $126.4 million, respectively, for the years ended December 31, 2017 and 2016.
(3) 
For the years ended December 31, 2017, 2016 and 2015 the total gain on disposal of assets for properties held in use and held for sale was $24.6 million and $40.5 million, $35.8 million and $16.6 million, and $34.5 million and $33.9 million, respectively.

Schedule of Minimum Future Contractual Rent to be Received Under Remaining Non-cancelable Term of Operating Leases
Scheduled minimum future contractual rent to be received under the remaining non-cancelable term of the operating leases (including realized rent increases occurring after January 1, 2018) are as follows (in thousands):
 
December 31,
2017
2018
$
599,194

2019
587,493

2020
570,820

2021
542,899

2022
507,936

Thereafter
3,637,342

Total future minimum rentals
$
6,445,684
Summary of Loans Receivable
The following table details loans receivable, net of premium and allowance for loan losses (in thousands):
 
December 31,
2017
 
December 31,
2016
Mortgage loans - principal
$
69,963

 
$
55,410

Mortgage loans - premium, net of amortization
5,038

 
7,194

Allowance for loan losses
(389
)
 
—

    Mortgages loans, net
74,612

 
62,604

Other note receivables - principal
5,355

 
4,474

Allowance for loan losses
—

 
(500
)
     Other note receivables
5,355

 
3,974

Total loans receivable, net
$
79,967

 
$
66,578
Summary of Lease Intangible, Net
The following table details lease intangible assets and liabilities, net of accumulated amortization (in thousands):
 
December 31,
2017
 
December 31,
2016
In-place leases
$
591,551

 
$
624,723

Above-market leases
89,640

 
88,873

Less: accumulated amortization
(271,288
)
 
(243,320
)
Intangible lease assets, net
$
409,903

 
$
470,276

 
 
 
 
Below-market leases
$
216,642

 
$
236,008

Less: accumulated amortization
(61,339
)
 
(53,688
)
Intangible lease liabilities, net
$
155,303

 
$
182,320
Schedule of Net Aggregate Amortization Expense of Intangible Assets and Liabilities
Based on the balance of intangible assets and liabilities at December 31, 2017, the net aggregate amortization expense for the next five years and thereafter is expected to be as follows (in thousands):
2018
$
32,343

2019
30,736

2020
28,717

2021
26,108

2022
22,838

Thereafter
113,858

Total future minimum amortization
$
254,600
Schedule of Components of Investment Assets held under Direct Financing Leases
The components of real estate investments held under direct financing leases were as follows (in thousands):
 
December 31,
2017
 
December 31, 2016
Minimum lease payments receivable
$
7,325

 
$
9,456

Estimated residual value of leased assets
24,552

 
35,640

Unearned income
(7,012
)
 
(9,091
)
Real estate assets under direct financing leases, net
$
24,865

 
$
36,005
Summary of Activity in Real Estate Assets Held for Sale
The following table shows the activity in real estate assets held for sale, net for the years ended December 31, 2017 and 2016:
 
Number of Properties
 
Carrying Value
 
(In Thousands)
Balance, December 31, 2015
36

 
$
84,259

Transfers from real estate investments
72

 
246,730

Sales
(59
)
 
(126,100
)
Transfers to real estate investments held and used
(5
)
 
(21,046
)
Impairments
—

 
(23,273
)
Balance, December 31, 2016
44

 
160,570

Transfers from real estate investments
82

 
216,502

Sales
(91
)
 
(208,029
)
Transfers to real estate investments held and used
(20
)
 
(95,382
)
Impairments
—

 
(24,732
)
Balance, December 31, 2017
15

 
$
48,929
Summary of Total Impairment Losses Recognized
The following table summarizes total impairment losses recognized in continuing and discontinued operations on the accompanying consolidated statements of operations (in thousands): 
 
Years Ended December 31,
 
2017
 
2016
 
2015
Real estate and intangible asset impairment
$
93,441

 
$
80,390

 
$
68,565

Write-off of lease intangibles, net
8,500

 
7,683

 
1,666

Loans receivable impairment
389

 
176

 
324

Total impairments from real estate investment net assets
102,330

 
88,249

 
70,555

Other impairment
—

 
26

 
174

Total impairment loss in continuing and discontinued operations
$
102,330

 
$
88,275

 
$
70,729