v3.19.3.a.u2

Unsecured Credit Agreements - Summary of Unsecured Credit Agreements (Parenthetical) (Detail) $ in Thousands	6 Months Ended		12 Months Ended
	Dec. 31, 2019 USD ($)	Jun. 30, 2019	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 31, 2019 Option	Jun. 23, 2017 Option
Debt Instrument [Line Items]
Carrying amount	$ 1,989,451		$ 1,989,451	$ 1,450,551
Maturity extension fee on outstanding principal balance percentage	0.05%		0.05%
2020 Unsecured Term Loan
Debt Instrument [Line Items]
Debt instrument extension options, description			two six-month extensions
1 Month LIBOR | 2019 Unsecured Term Loan
Debt Instrument [Line Items]
Number of option available to extend maturity period | Option					2
Revolving Credit Facility | Unsecured Revolving Credit and Term Loan Agreement
Debt Instrument [Line Items]
Number of option available to extend maturity period | Option						1
2024 Unsecured Term Loan | Unsecured Revolving Credit and Term Loan Agreement
Debt Instrument [Line Items]
Basis spread on variable rate				1.90%
2024 Unsecured Term Loan | Unsecured Revolving Credit and Term Loan Agreement | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	0.85%	1.50%		1.90%
2024 Unsecured Term Loan | Unsecured Revolving Credit and Term Loan Agreement | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	1.65%	2.45%
Unsecured Debt
Debt Instrument [Line Items]
Carrying amount	$ 1,877,300		$ 1,877,300	$ 1,371,100
Unsecured Debt | Unsecured Revolving Credit and Term Loan Agreement
Debt Instrument [Line Items]
Carrying amount	652,300		652,300	596,100
Unsecured Debt | 2019 Unsecured Term Loan
Debt Instrument [Line Items]
Carrying amount				$ 300,000
Unsecured Debt | 2020 Unsecured Term Loan
Debt Instrument [Line Items]
Carrying amount	$ 300,000		$ 300,000
Basis spread on variable rate			1.25%
Unsecured Debt | 1 Month LIBOR
Debt Instrument [Line Items]
Interest rate	1.76%		1.76%	2.35%
Unsecured Debt | 1 Month LIBOR | 2019 Unsecured Term Loan
Debt Instrument [Line Items]
Basis spread on variable rate			1.40%
Unsecured Debt | Swingline Revolving Credit Facility
Debt Instrument [Line Items]
Carrying amount				$ 15,000
Unsecured Debt | Swingline Revolver | 2012 Unsecured Credit Agreement
Debt Instrument [Line Items]
Carrying amount				$ 15,000
Basis spread on variable rate				5.45%
Unsecured Debt | Revolving Credit Facility | Unsecured Revolving Credit and Term Loan Agreement
Debt Instrument [Line Items]
Carrying amount	$ 197,300		$ 197,300	$ 141,100
Unsecured Debt | Revolving Credit Facility | 1 Month LIBOR | 2012 Unsecured Credit Agreement
Debt Instrument [Line Items]
Carrying amount				$ 126,100
Basis spread on variable rate				1.20%
Unsecured Debt | Revolving Credit Facility | 1 Month LIBOR | Unsecured Revolving Credit and Term Loan Agreement
Debt Instrument [Line Items]
Basis spread on variable rate			1.20%
Unsecured Debt | 2024 Unsecured Term Loan | Unsecured Revolving Credit and Term Loan Agreement
Debt Instrument [Line Items]
Carrying amount	$ 190,000		$ 190,000	$ 190,000
Unsecured Debt | 2024 Unsecured Term Loan | 1 Month LIBOR | Unsecured Revolving Credit and Term Loan Agreement
Debt Instrument [Line Items]
Basis spread on variable rate			1.25%

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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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