Annual report pursuant to Section 13 and 15(d)

Unsecured Line of Credit and Term Notes - Borrowings Outstanding on Unsecured Line of Credit and Term Notes (Detail)

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Unsecured Line of Credit and Term Notes - Borrowings Outstanding on Unsecured Line of Credit and Term Notes (Detail) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Debt Instrument [Line Items]    
Revolving line of credit borrowings $ 91,000 $ 105,000
Total term note principal balance outstanding 1,625,000 1,625,000
Less: unamortized debt issuance costs (9,778) (10,962)
Less: unamortized senior term note discount (4,402) (4,949)
Term notes payable 1,610,820 1,609,089
Term Note Due June 4, 2020 [Member]    
Debt Instrument [Line Items]    
Total term note principal balance outstanding 100,000 100,000
Term Note Due August 5, 2021 [Member]    
Debt Instrument [Line Items]    
Total term note principal balance outstanding 100,000 100,000
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