Debt - Unsecured Revolving Credit Facility and Term Loan Narrative (Details)	Feb. 08, 2019 USD ($) extension_option	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Line of Credit Facility [Line Items]
Outstanding amounts		$ 670,000,000	$ 550,000,000
Outstanding borrowings		665,836,000	545,594,000
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		170,000,000	50,000,000
Outstanding borrowings		170,000,000	50,000,000
New Term Loan
Line of Credit Facility [Line Items]
Outstanding amounts		200,000,000	200,000,000
Outstanding borrowings		$ 198,978,000	$ 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%