Debt - Unsecured Revolving Credit Facility and Term Loan Narrative (Details)		1 Months Ended	6 Months Ended
	Feb. 08, 2019 USD ($) extension_option	Aug. 05, 2021 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Line of Credit Facility [Line Items]
Outstanding amounts			$ 950,000,000		$ 550,000,000
Outstanding borrowings			939,921,000		545,594,000
Borrowings under unsecured revolving credit facility			170,000,000	$ 15,000,000
Revolving credit facility | New Revolving Facility
Line of Credit Facility [Line Items]
Credit facility borrowing capacity	$ 600,000,000.0
Number of extension options | extension_option	2
Extension option term (in months)	6 months
Revolving credit facility | New Revolving Facility | Minimum
Line of Credit Facility [Line Items]
Facility fee on revolving commitment fees (percent)	0.15%
Facility fee on revolving commitment fee based on investment grade ratings (percent)	0.125%
Revolving credit facility | New Revolving Facility | Minimum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	0.10%
Revolving credit facility | New Revolving Facility | Minimum | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	1.10%
Revolving credit facility | New Revolving Facility | Maximum
Line of Credit Facility [Line Items]
Facility fee on revolving commitment fees (percent)	0.35%
Facility fee on revolving commitment fee based on investment grade ratings (percent)	0.30%
Revolving credit facility | New Revolving Facility | Maximum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	0.55%
Revolving credit facility | New Revolving Facility | Maximum | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	1.55%
Letter of credit
Line of Credit Facility [Line Items]
Subfacility capacity as percentage of available revolving commitments (percent)	10.00%
Swingline loan
Line of Credit Facility [Line Items]
Subfacility capacity as percentage of available revolving commitments (percent)	10.00%
Revolving Facility
Line of Credit Facility [Line Items]
Outstanding amounts			50,000,000		50,000,000
Outstanding borrowings			50,000,000		50,000,000
Revolving Facility | Subsequent event
Line of Credit Facility [Line Items]
Borrowings under unsecured revolving credit facility		$ 50,000,000.0
New Term Loan
Line of Credit Facility [Line Items]
Outstanding amounts			200,000,000		200,000,000
Outstanding borrowings			$ 199,031,000		$ 198,925,000
New Term Loan | Term Loan
Line of Credit Facility [Line Items]
Debt instrument face amount	$ 200,000,000.0
New Term Loan | Term Loan | Minimum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	0.50%
New Term Loan | Term Loan | Minimum | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	1.50%
New Term Loan | Term Loan | Maximum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	1.20%
New Term Loan | Term Loan | Maximum | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	2.20%