Unsecured Lines of Credit Payable - Narrative (Details)		3 Months Ended	9 Months Ended
	Sep. 30, 2020 USD ($)	Mar. 31, 2018 USD ($) extension_option	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Mar. 29, 2018 USD ($)	Jul. 22, 2016 USD ($)	Sep. 15, 2015 USD ($)
Line of Credit Facility [Line Items]
Repayments of unsecured debt			$ 250,000,000	$ 450,000,000
Credit Agreement 2018
Line of Credit Facility [Line Items]
Credit agreement, aggregate maximum borrowing capacity including accordion feature		$ 1,500,000,000
2015 Term Loan
Line of Credit Facility [Line Items]
Debt instrument face amount							$ 150,000,000.0
2015 Term Loan | Interest Rate Swap
Line of Credit Facility [Line Items]
Derivative notional amount	$ 150,000,000		$ 150,000,000				$ 150,000,000.0
Derivative, fixed interest rate (percent)							2.72%
2018 Term Loan
Line of Credit Facility [Line Items]
Debt instrument face amount					$ 250,000,000.0
2018 Term Loan | Interest Rate Swap
Line of Credit Facility [Line Items]
Derivative, fixed interest rate (percent)	2.87%		2.87%		2.87%
2018 Term Loan A | Interest Rate Swap
Line of Credit Facility [Line Items]
Derivative notional amount	$ 150,000,000.0		$ 150,000,000.0		$ 150,000,000.0
Derivative, fixed interest rate (percent)	2.31%		2.31%		2.31%
2018 Term Loan B
Line of Credit Facility [Line Items]
Debt instrument face amount					$ 100,000,000.0
2018 Term Loan B | Interest Rate Swap
Line of Credit Facility [Line Items]
Derivative notional amount	$ 100,000,000.0		$ 100,000,000.0		$ 100,000,000.0
Derivative, fixed interest rate (percent)	3.71%		3.71%		3.71%
2016 Term Loan
Line of Credit Facility [Line Items]
Debt instrument face amount						$ 150,000,000.0
2016 Term Loan | Interest Rate Swap
Line of Credit Facility [Line Items]
Derivative notional amount						$ 150,000,000.0
Derivative, fixed interest rate (percent)						2.86%
Term Loan | 2015 Term Loan
Line of Credit Facility [Line Items]
Debt instrument face amount		150,000,000.0
Term Loan | 2018 Term Loan
Line of Credit Facility [Line Items]
Debt instrument face amount		250,000,000.0
Term Loan | 2018 Term Loan | LIBOR | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			0.85%
Term Loan | 2018 Term Loan | LIBOR | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			1.75%
Term Loan | 2018 Term Loan | Base Rate | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			0.00%
Term Loan | 2018 Term Loan | Base Rate | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			0.75%
Term Loan | 2016 Term Loan
Line of Credit Facility [Line Items]
Repayments of unsecured debt		150,000,000.0
Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility borrowing capacity	$ 700,000,000	$ 700,000,000.0	$ 700,000,000
Debt instrument term		4 years
Number of extensions allowed | extension_option		2
Term of allowable extensions (in months)		6 months
Commitment fee (percent)	0.20%
One-month LIBOR (percent)	0.15%		0.15%
Repayment of borrowings on credit facility		$ 100,000,000.0	$ 269,000,000
Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Commitment fee (percent)			0.10%
Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Commitment fee (percent)			0.30%
Revolving Credit Facility | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	1.00%
Base rate component, spread on variable rate (percent)			1.00%
Revolving Credit Facility | LIBOR | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			0.775%
Revolving Credit Facility | LIBOR | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			1.55%
Revolving Credit Facility | Base Rate | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			0.00%
Revolving Credit Facility | Base Rate | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			0.55%
Revolving Credit Facility | Federal Funds Rate
Line of Credit Facility [Line Items]
Base rate component, spread on variable rate (percent)			0.50%