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

Settlement of Forward Swaps

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Amount of the required periodic payments applied to principal.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount, after accumulated amortization, of debt discount.

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Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount of investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

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Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

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Cash inflow associated with loan origination (the process when securing a mortgage for a piece of real property) or lease origination.

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The cash outflow to repay long-term debt that is not secured by collateral. Excludes repayments of tax exempt unsecured debt.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

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