Fair Value Measurements - Carrying Values and Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	$ 40,102
Debt instrument, unamortized discount	26,464
Carrying Value \| Level 2
Assets carried at historical cost on the consolidated balance sheets
Investments in debt securities	378,545	$ 209,337
Fair Value \| Level 2
Assets carried at historical cost on the consolidated balance sheets
Investments in debt securities	379,500	209,390
Mortgage Loans
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	28,075	9,256
Debt instrument, unamortized discount	0
Mortgage Loans \| Carrying Value \| Level 2
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	7,608,228	5,263,994
Mortgage Loans \| Fair Value \| Level 2
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	7,627,423	5,265,180
Term Loan Facility
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	12,027
Debt instrument, unamortized discount	0
Term Loan Facility \| Carrying Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	1,500,000	0
Term Loan Facility \| Fair Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	1,494,494	0
Revolving Credit Facility \| Carrying Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	35,000	0
Revolving Credit Facility \| Fair Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	35,007	0
Convertible Senior Notes
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	0
Debt instrument, unamortized discount	26,464
Convertible Senior Notes \| Carrying Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	548,536	0
Convertible Senior Notes \| Fair Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	557,179	0
Credit facilities
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	0	6,044
Credit facilities \| Carrying Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	0	2,321,585
Credit facilities \| Fair Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	$ 0	$ 2,329,551

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Amount, after accumulated amortization, of debt discount.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

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-Publisher FASB
-Name Accounting Standards Codification
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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Fair value of investments in debt securities classified as held-to-maturity.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 320
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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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