Debt - Unsecured Revolving Credit Facility and Term Loan Narrative (Details)	Feb. 08, 2019 USD ($) extension_option	Feb. 01, 2016 USD ($) extension_option	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Line of Credit Facility [Line Items]
Principal outstanding			$ 560,000,000	$ 495,000,000
Borrowings outstanding			554,624,000	489,765,000
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
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%
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%
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]
Principal outstanding			60,000,000	95,000,000
Borrowings outstanding			60,000,000	95,000,000
Revolving Facility | Prior Term Loan
Line of Credit Facility [Line Items]
Credit facility borrowing capacity		$ 100,000,000.0
Credit facility prepayment premium in first year (percent)		2.00%
Credit facility prepayment premium in second year (percent)		1.00%
Revolving Facility | Prior Revolving Facility
Line of Credit Facility [Line Items]
Credit facility borrowing capacity		$ 400,000,000.0
Credit facility uncommitted incremental facility		$ 250,000,000.0
Number of extension options | extension_option		2
Extension option term (in months)		6 months
Unsecured Debt | New Term Loan Feb 2019
Line of Credit Facility [Line Items]
Debt instrument face amount	$ 200,000,000.0
Unsecured Debt | New Term Loan Feb 2019 | Maximum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	1.20%
Unsecured Debt | New Term Loan Feb 2019 | Maximum | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	2.20%
Unsecured Debt | New Term Loan Feb 2019 | Minimum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	0.50%
Unsecured Debt | New Term Loan Feb 2019 | Minimum | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	1.50%
Senior Unsecured Term Loan
Line of Credit Facility [Line Items]
Principal outstanding			200,000,000	100,000,000
Borrowings outstanding			$ 198,713,000	$ 99,612,000