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Borrowings - Additional Information (Detail) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 USD ($) | Sep. 30, 2018 USD ($)
Debt Instrument [Line Items] |  |
Notes Payable | $ 4,504,023 | $ 4,504,023
Debt Instrument, Interest Rate, Effective Percentage | 3.70% | 3.70%
Mortgages [Member] |  |
Debt Instrument [Line Items] |  |
Proceeds from Loan Originations |  | $ 38,300
Debt Instrument, Periodic Payment, Principal |  | $ 7,900
Secured Debt [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Effective Percentage | 3.90% | 3.90%
Secured Debt [Member] | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member] |  |
Debt Instrument [Line Items] |  |
Line of Credit Facility, Maximum Borrowing Capacity | $ 80,000 | $ 80,000
Line of Credit Facility, Amount Outstanding | $ 80,000 | $ 80,000
Secured Debt [Member] | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member] | Variable Rate Debt [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Effective Percentage | 2.70% | 2.70%
Secured Debt [Member] | Mortgages [Member] | Fixed Rate Debt |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Effective Percentage | 4.00% | 4.00%
Debt Instrument, Maturity Date |  | Nov. 01, 2019
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate | $ 836,513 | $ 836,513
Unsecured Debt [Member] |  |
Debt Instrument [Line Items] |  |
Notes Payable | $ 3,582,624 | $ 3,582,624
Debt Instrument, Interest Rate, Effective Percentage | 3.70% | 3.70%
Unsecured Debt [Member] | Wells Fargo Term Loan [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Face Amount | $ 300,000 | $ 300,000
Unsecured Debt [Member] | US Bank Term Loan [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Face Amount | $ 150,000 | $ 150,000
Unsecured Debt [Member] | $1 billion unsecured revolving credit faciltiy [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Effective Percentage | 3.06% | 3.06%
Letters of Credit Outstanding, Amount | $ 1,900 | $ 1,900
Unsecured Debt [Member] | $1 billion unsecured revolving credit faciltiy [Member] | Variable Rate Debt [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Effective Percentage | 3.10% | 3.10%
Debt Instrument, Maturity Date |  | Apr. 15, 2020
Line of Credit Facility, Amount Outstanding | $ 370,000 | $ 370,000
Unsecured Debt [Member] | Variable Rate Debt [Member] |  |
Debt Instrument [Line Items] |  |
Unsecured notes payable | $ 300,000 | $ 300,000
Debt Instrument, Interest Rate, Effective Percentage | 3.10% | 3.10%
Debt Instrument, Maturity Date |  | Aug. 29, 2020
Unsecured Debt [Member] | KeyBank Term Loan [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Face Amount | $ 150,000 | $ 150,000
Unsecured Debt [Member] | Public Income Notes [Member] | Fixed Rate Debt |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Face Amount | 2,400,000 | 2,400,000
Unsecured Debt [Member] | Private Placement [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Face Amount | 242,000 | 242,000
Unsecured Debt [Member] | Private Placement [Member] | Fixed Rate Debt |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Face Amount | 242,000 | 242,000
Repayments of Unsecured Debt | 50,000 |
Unsecured Debt [Member] | 4.2% Notes due 2028 [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Face Amount | $ 400,000 | $ 400,000
Debt Instrument, Interest Rate, Stated Percentage | 4.20% | 4.20%
Debt Instrument, Redemption Price, Percentage |  | 99.403%
Debt Instrument, Unamortized Discount | $ 2,400 | $ 2,400
Debt Issuance Costs, Gross | $ 2,600 | 2,600
Proceeds from Debt, Net of Issuance Costs |  | 395,000
Settlement of Forward Swaps |  | $ 200,000
Debt Instrument, Term |  | 10 years
Debt Instrument, Interest Rate, Effective Percentage | 4.21% | 4.21%
Unsecured Debt [Member] | $1 billion unsecured revolving credit facility [Member] |  |
Debt Instrument [Line Items] |  |
Line of Credit Facility, Current Borrowing Capacity | $ 1,000,000 | $ 1,000,000
Line of Credit Facility, Maximum Borrowing Capacity | 1,500,000 | 1,500,000
Line of Credit Facility, Amount Outstanding | 370,000 | 370,000
Unsecured Debt [Member] | Term Loan [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Face Amount | $ 300,000 | $ 300,000
Debt Instrument, Interest Rate, Effective Percentage | 2.30% | 2.30%
Debt Instrument, Maturity Date |  | Mar. 01, 2022
Unsecured Debt [Member] | Wells Fargo Term Loan 2018 [Domain] |  |
Debt Instrument [Line Items] |  |
Repayments of Unsecured Debt | $ 250,000 |
Minimum [Member] | Unsecured Debt [Member] | Fixed Rate Debt |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Term |  | 7 years
Minimum [Member] | Unsecured Debt [Member] | US Bank Term Loan [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Basis Spread on Variable Rate |  | 0.90%
Minimum [Member] | Unsecured Debt [Member] | KeyBank Term Loan [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Basis Spread on Variable Rate |  | 0.90%
Minimum [Member] | Unsecured Debt [Member] | $1 billion unsecured revolving credit facility [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Basis Spread on Variable Rate |  | 0.85%
Minimum [Member] | Unsecured Debt [Member] | Term Loan [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Basis Spread on Variable Rate |  | 0.90%
Maximum [Member] | Unsecured Debt [Member] | Fixed Rate Debt |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Term |  | 12 years
Maximum [Member] | Unsecured Debt [Member] | US Bank Term Loan [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Basis Spread on Variable Rate |  | 1.90%
Maximum [Member] | Unsecured Debt [Member] | KeyBank Term Loan [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Basis Spread on Variable Rate |  | 1.75%
Maximum [Member] | Unsecured Debt [Member] | $1 billion unsecured revolving credit facility [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Basis Spread on Variable Rate |  | 1.55%
Maximum [Member] | Unsecured Debt [Member] | Term Loan [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Basis Spread on Variable Rate |  | 1.75%
years to maturity [Member] | Unsecured Debt [Member] | Fixed Rate Debt |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Term |  | 6 years 9 months 15 days

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