Investments (Tables)
 12 Months Ended
Dec. 31, 2018
Real Estate [Abstract]  
Summary of Gross Real Estate and Loan Activity
During the years ended December 31, 2018 and 2017, 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, 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

Acquisitions/improvements (1)
21

 
2

 
23

 
308,985

 
37,888

 
346,873

Dispositions of real estate (2)(3)
(52
)
 
(5
)
 
(57
)
 
(126,961
)
 
—

 
(126,961
)
Principal payments and payoffs
—

 
(31
)
 
(31
)
 
—

 
(30,863
)
 
(30,863
)
Impairments
—

 
—

 
—

 
(17,668
)
 
—

 
(17,668
)
Write-off of gross lease intangibles
—

 
—

 
—

 
(54,820
)
 
—

 
(54,820
)
Loan premium amortization and other
—

 
—

 
—

 
(955
)
 
(2,060
)
 
(3,015
)
Spin-off to SMTA
(899
)
 
(2
)
 
(901
)
 
(2,855,052
)
 
(37,888
)
 
(2,892,940
)
Gross balance, December 31, 2018
1,462

 
52

 
1,514

 
$
5,076,587

 
$
47,044

 
$
5,123,631

Accumulated depreciation and amortization
 
 
 
 
 
 
(727,533
)
 
—

 
(727,533
)
Net balance, December 31, 2018
 
 
 
 
 
 
$
4,349,054

 
$
47,044

 
$
4,396,098


(1) 
Includes investments of $46.0 million and $42.6 million, respectively, in revenue producing capitalized expenditures, as well as $6.3 million and $3.5 million, respectively, of non-revenue producing capitalized expenditures for the years ended December 31, 2018 and 2017.
(2) 
The total accumulated depreciation and amortization associated with dispositions of real estate was $19.5 million and $57.1 million, respectively, for the years ended December 31, 2018 and 2017.
(3) 
The total gain on disposal of assets for properties held in use was $1.4 million, $24.6 million and $35.8 million for the years ended December 31, 2018, 2017 and 2016, respectively. The total gain on disposal of assets for properties held for sale was $13.0 million, $40.5 million and $16.6 million for the years ended December 31, 2018, 2017 and 2016, 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, 2019) are as follows (in thousands):
 
December 31,
2018
2019
$
379,353

2020
374,010

2021
354,562

2022
332,489

2023
308,001

Thereafter
2,180,140

Total future minimum rentals
$
3,928,555
Summary of Loans Receivable
The following table details loans receivable, net of premiums, discounts and allowance for loan losses (in thousands):
 
December 31,
2018
 
December 31,
2017
Mortgage loans - principal
$
42,660

 
$
69,963

Mortgage loans - premium, net of amortization
2,527

 
5,038

Allowance for loan losses
—

 
(389
)
    Mortgage loans, net
45,187

 
74,612

Other note receivables - principal
2,082

 
5,355

Other note receivables - discount, net of amortization
(225
)
 
—

     Other note receivables
1,857

 
5,355

Total loans receivable, net
$
47,044

 
$
79,967
Summary of Lease Intangible, Net
The following table details lease intangible assets and liabilities, net of accumulated amortization (in thousands):
 
December 31,
2018
 
December 31,
2017
In-place leases
$
381,143

 
$
591,551

Above-market leases
62,902

 
89,640

Less: accumulated amortization
(149,582
)
 
(271,288
)
Intangible lease assets, net
$
294,463

 
$
409,903

 
 
 
 
Below-market leases
$
167,527

 
$
216,642

Less: accumulated amortization
(47,365
)
 
(61,339
)
Intangible lease liabilities, net
$
120,162

 
$
155,303
Schedule of Net Aggregate Amortization Expense of Intangible Assets and Liabilities
Based on the balance of intangible assets and liabilities at December 31, 2018, the net aggregate amortization expense for the next five years and thereafter is expected to be as follows (in thousands):
2019
$
22,538

2020
21,650

2021
20,034

2022
17,658

2023
16,472

Thereafter
75,949

Total future minimum amortization
$
174,301
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,
2018
 
December 31, 2017
Minimum lease payments receivable
$
5,390

 
$
7,325

Estimated residual value of leased assets
20,097

 
24,552

Unearned income
(5,198
)
 
(7,012
)
Real estate assets under direct financing leases, net
$
20,289

 
$
24,865
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, 2018 and 2017:
 
Number of Properties
 
Carrying Value
 
(In Thousands)
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

Transfers from real estate investments
9

 
39,488

Sales
(9
)
 
(35,657
)
Transfers to real estate investments held and used
(7
)
 
(25,715
)
Transfers to SMTA
(5
)
 
(7,853
)
Impairments
—

 
(989
)
Balance, December 31, 2018
3

 
$
18,203
Summary of Total Impairment Losses Recognized
The following table summarizes total impairments recognized in continuing and discontinued operations on the accompanying consolidated statements of operations (in thousands): 
 
Years Ended December 31,
 
2018
 
2017
 
2016
Real estate and intangible asset impairment
$
17,208

 
$
93,441

 
$
80,390

Write-off of lease intangibles, net
477

 
8,500

 
7,683

Loans receivable (recovery) impairment
(17
)
 
389

 
176

Total impairments from real estate investment net assets
17,668

 
102,330

 
88,249

Other impairment
—

 
—

 
26

Total impairments
$
17,668

 
$
102,330

 
$
88,275