Borrowings - Additional Information (Detail) $ in Thousands	6 Months Ended
Jun. 30, 2018 USD ($)
Debt Instrument [Line Items]
Notes Payable	$ 4,548,635
Debt Instrument, Interest Rate, Effective Percentage	3.70%
Mortgages [Member]
Debt Instrument [Line Items]
Proceeds from Loan Originations	$ 38,300
Debt Instrument, Periodic Payment, Principal	$ 5,300
Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	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
Line of Credit Facility, Amount Outstanding	$ 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	2.50%
Secured Debt [Member] \| Mortgages [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	4.00%
Debt Instrument, Maturity Date	Nov. 01, 2019
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate	$ 839,131
Unsecured Debt [Member]
Debt Instrument [Line Items]
Notes Payable	$ 3,621,824
Debt Instrument, Interest Rate, Effective Percentage	3.70%
Unsecured Debt [Member] \| Wells Fargo Term Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 300,000
Unsecured Debt [Member] \| US Bank Term Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 150,000
Unsecured Debt [Member] \| $1 billion unsecured revolving credit faciltiy [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	2.99%
Letters of Credit Outstanding, Amount	$ 2,600
Unsecured Debt [Member] \| $1 billion unsecured revolving credit faciltiy [Member] \| Variable Rate Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	3.00%
Debt Instrument, Maturity Date	Apr. 15, 2020
Line of Credit Facility, Amount Outstanding	$ 110,000
Unsecured Debt [Member] \| Variable Rate Debt [Member]
Debt Instrument [Line Items]
Unsecured notes payable	$ 300,000
Debt Instrument, Interest Rate, Effective Percentage	2.90%
Debt Instrument, Maturity Date	Aug. 29, 2020
Unsecured Debt [Member] \| KeyBank Term Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 150,000
Unsecured Debt [Member] \| Public Income Notes [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount	2,400,000
Unsecured Debt [Member] \| Private Placement [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	292,000
Unsecured Debt [Member] \| Private Placement [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount	292,000
Unsecured Debt [Member] \| 4.2% Notes due 2028 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 400,000
Debt Instrument, Interest Rate, Stated Percentage	4.20%
Debt Instrument, Redemption Price, Percentage	99.403%
Debt Instrument, Unamortized Discount	$ 2,400
Debt Issuance Costs, Gross	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%
Unsecured Debt [Member] \| $1 billion unsecured revolving credit facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 1,000,000
Line of Credit Facility, Maximum Borrowing Capacity	1,500,000
Line of Credit Facility, Amount Outstanding	110,000
Unsecured Debt [Member] \| Term Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 550,000
Debt Instrument, Interest Rate, Effective Percentage	2.90%
Debt Instrument, Maturity Date	Jul. 14, 2020
Minimum [Member] \| Unsecured Debt [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
Debt Instrument, Term	7 years
Minimum [Member] \| Unsecured Debt [Member] \| Wells Fargo Term Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.90%
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] \| Wells Fargo Term Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.90%
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 10 months 15 days

Settlement of Forward Swaps

No definition available.

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

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No definition available.

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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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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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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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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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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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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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