Debt (Schedule of Current Senior Notes Outstanding) (Details) - Senior Notes	Sep. 30, 2020 USD ($)	Sep. 30, 2020 EUR (€)	Apr. 14, 2020 USD ($)	Apr. 10, 2020	Apr. 02, 2020 USD ($)
2023 Series A Notes
Line of Credit Facility [Line Items]
Principal Amount	$ 75,000,000
Coupon Rate	3.94%	3.94%
2025 Series B Notes
Line of Credit Facility [Line Items]
Principal Amount	$ 75,000,000
Coupon Rate	4.04%	4.04%
2026 Senior Notes
Line of Credit Facility [Line Items]
Principal Amount	$ 75,000,000
Coupon Rate	3.72%	3.72%
2021 Series A Notes
Line of Credit Facility [Line Items]
Principal Amount	$ 50,000,000
Coupon Rate	3.32%	3.32%
2024 Series B Notes
Line of Credit Facility [Line Items]
Principal Amount	$ 75,000,000
Coupon Rate	3.76%	3.76%
2025 Series C Notes
Line of Credit Facility [Line Items]
Principal Amount | €		€ 88,857,000
Coupon Rate	1.785%	1.785%
2022 Series A Notes
Line of Credit Facility [Line Items]
Principal Amount	$ 75,000,000
Coupon Rate	3.25%	3.25%
2027 Series B Notes
Line of Credit Facility [Line Items]
Principal Amount	$ 75,000,000
Coupon Rate	3.72%	3.72%
2029 Series C Notes
Line of Credit Facility [Line Items]
Principal Amount	$ 100,000,000
Coupon Rate	4.19%	4.19%
MetLife 2030 Series D Notes
Line of Credit Facility [Line Items]
Principal Amount	$ 125,000,000				$ 125,000,000
Coupon Rate	2.50%	2.50%			2.50%
Prudential 2030 Series D Notes
Line of Credit Facility [Line Items]
Principal Amount	$ 75,000,000		$ 75,000,000
Coupon Rate	2.50%	2.50%		2.50%