Unsecured Line of Credit and Term Notes - Borrowings Outstanding on Unsecured Line of Credit and Term Notes (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Revolving line of credit borrowings	$ 43,000
Total term note principal balance outstanding	2,175,000	$ 2,175,000
Less: unamortized debt issuance costs	(12,380)	(12,833)
Less: unamortized senior term note discount	(6,480)	(6,710)
Term notes payable	2,156,140	2,155,457
Term Note Due April 8, 2024 [Member]
Debt Instrument [Line Items]
Total term note principal balance outstanding	175,000	175,000
Senior Term Note Due July 1, 2026 [Member]
Debt Instrument [Line Items]
Total term note principal balance outstanding	600,000	600,000
Senior Term Note Due December 15, 2027 [Member]
Debt Instrument [Line Items]
Total term note principal balance outstanding	450,000	450,000
Term Note Due July 21, 2028 [Member]
Debt Instrument [Line Items]
Total term note principal balance outstanding	200,000	200,000
Senior Term Note Due June 15, 2029 [Member]
Debt Instrument [Line Items]
Total term note principal balance outstanding	350,000	350,000
Senior Term Note Due October 15, 2030 [Member]
Debt Instrument [Line Items]
Total term note principal balance outstanding	$ 400,000	$ 400,000

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after accumulated amortization, of debt discount.

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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.

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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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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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