Long-Term Debt Shelf Arrangements (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Line of Credit Facility [Line Items]
Long-term Debt	$ (568,800)	$ (523,000)
Debt Instrument, Unused Borrowing Capacity, Amount	250,000
Prudential [Member]
Line of Credit Facility [Line Items]
Long-term Debt	(220,000)
Debt Instrument, Unused Borrowing Capacity, Amount	150,000
MetLife [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount	150,000
Debt Instrument, Unused Borrowing Capacity, Amount	100,000
Aggregate Shelf Agreements [Member]
Line of Credit Facility [Line Items]
Long-term Debt	(220,000)
Aggregated Unfunded Commitments [Member]
Line of Credit Facility [Line Items]
Long-term Debt	(50,000)
Aggregated Unfunded Commitments [Member] | MetLife [Member]
Line of Credit Facility [Line Items]
Long-term Debt	(50,000)
Uncollateralized Senior Note Due April Two Thousand Thirty Two [Member]
Line of Credit Facility [Line Items]
Long-term Debt	$ (70,000)	(70,000)
Debt Instrument, Interest Rate, Stated Percentage	3.25%
Uncollateralized Senior Note Due August Two Thousand Thirty Nine [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.98%
Uncollateralized Senior Note Due July Two Thousand Thirty Five
Line of Credit Facility [Line Items]
Long-term Debt	$ (50,000)	(50,000)
Debt Instrument, Interest Rate, Stated Percentage	3.00%
Uncollateralized Senior Note Due August Two Thousand Thirty Five
Line of Credit Facility [Line Items]
Long-term Debt	$ (40,000)	$ (40,000)
Debt Instrument, Interest Rate, Stated Percentage	2.96%
Maximum [Member] | Prudential [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount	$ 370,000
Maximum [Member] | Aggregate Shelf Agreements [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount	$ 520,000