Fair Value Measurements - Carrying Values and Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	$ 48,470
Debt instrument, unamortized discount	24,298	$ 26,464
Carrying Value \| Level 2
Assets carried at historical cost on the consolidated balance sheets
Investments in debt securities	424,351	378,545
Fair Value \| Level 2
Assets carried at historical cost on the consolidated balance sheets
Investments in debt securities	422,162	379,500
Mortgage Loans
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	37,165	28,075
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	7,651,625	7,608,228
Mortgage Loans \| Fair Value \| Level 2
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	7,612,163	7,627,423
Term Loan Facility
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	11,305
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	1,500,000
Term Loan Facility \| Fair Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	1,495,193	1,494,494
Revolving Credit Facility \| Carrying Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	15,000	35,000
Revolving Credit Facility \| Fair Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	15,006	35,007
Convertible Senior Notes
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	0
Debt instrument, unamortized discount	24,298
Convertible Senior Notes \| Carrying Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	550,695	548,536
Convertible Senior Notes \| Fair Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	534,101	557,179
Revolving Facility
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	0
Debt instrument, unamortized discount	0
Term Loan Facility \| Revolving Facility
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	$ 11,305	$ 12,027

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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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-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
-Name Accounting Standards Codification
-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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