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Fair Value Measurement (Quantitative Information Regarding Level 3 Valuations) (Details) $ in Thousands	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Assets:
Estimated Fair Value	$ 3,355,312	$ 3,472,472
Other investments	264,681	262,485
Level 3
Assets:
Equity investments	5,233	2,803
Other investments	2,388	1,783
Liabilities:
Other liabilities	$ 9,500	15,000
Level 3 | Comparability Adjustment | Discounted Cash Flows | Minimum
Assets:
Equity securities measured at fair value	0
Other investments, measurement input	0
Level 3 | Comparability Adjustment | Discounted Cash Flows | Maximum
Assets:
Equity securities measured at fair value	0.10
Other investments, measurement input	0.10
Level 3 | Comparability Adjustment | Discounted Cash Flows | Weighted Average
Assets:
Equity securities measured at fair value	0.05
Other investments, measurement input	0.05
Level 3 | Comparability Adjustment | Stochastic Model/Discounted Cash Flows | Minimum
Liabilities:
Other liabilities, measurement input	0.00%
Level 3 | Comparability Adjustment | Stochastic Model/Discounted Cash Flows | Maximum
Liabilities:
Other liabilities, measurement input	10.00%
Level 3 | Comparability Adjustment | Stochastic Model/Discounted Cash Flows | Weighted Average
Liabilities:
Other liabilities, measurement input	9.00%
Corporate debt, limited observable inputs | Level 3
Assets:
Estimated Fair Value	$ 65,960	63,973
Corporate debt, limited observable inputs | Level 3 | Comparability Adjustment | Market Comparable Securities | Minimum
Assets:
Assets measured at fair value	0
Corporate debt, limited observable inputs | Level 3 | Comparability Adjustment | Market Comparable Securities | Maximum
Assets:
Assets measured at fair value	0.05
Corporate debt, limited observable inputs | Level 3 | Comparability Adjustment | Market Comparable Securities | Weighted Average
Assets:
Assets measured at fair value	0.025
Corporate debt, limited observable inputs | Level 3 | Comparability Adjustment | Discounted Cash Flows | Minimum
Assets:
Assets measured at fair value	0
Corporate debt, limited observable inputs | Level 3 | Comparability Adjustment | Discounted Cash Flows | Maximum
Assets:
Assets measured at fair value	0.05
Corporate debt, limited observable inputs | Level 3 | Comparability Adjustment | Discounted Cash Flows | Weighted Average
Assets:
Assets measured at fair value	0.025
Residential mortgage-backed securities | Level 3
Assets:
Estimated Fair Value	$ 271	249
Residential mortgage-backed securities | Level 3 | Comparability Adjustment | Market Comparable Securities | Minimum
Assets:
Assets measured at fair value	0
Residential mortgage-backed securities | Level 3 | Comparability Adjustment | Market Comparable Securities | Maximum
Assets:
Assets measured at fair value	0.05
Residential mortgage-backed securities | Level 3 | Comparability Adjustment | Market Comparable Securities | Weighted Average
Assets:
Assets measured at fair value	0.025
Residential mortgage-backed securities | Level 3 | Comparability Adjustment | Discounted Cash Flows | Minimum
Assets:
Assets measured at fair value	0
Residential mortgage-backed securities | Level 3 | Comparability Adjustment | Discounted Cash Flows | Maximum
Assets:
Assets measured at fair value	0.05
Residential mortgage-backed securities | Level 3 | Comparability Adjustment | Discounted Cash Flows | Weighted Average
Assets:
Assets measured at fair value	0.025
Other asset-backed securities | Level 3
Assets:
Estimated Fair Value	$ 941	$ 2,705
Other asset-backed securities | Level 3 | Comparability Adjustment | Market Comparable Securities | Minimum
Assets:
Assets measured at fair value	0
Other asset-backed securities | Level 3 | Comparability Adjustment | Market Comparable Securities | Maximum
Assets:
Assets measured at fair value	0.05
Other asset-backed securities | Level 3 | Comparability Adjustment | Market Comparable Securities | Weighted Average
Assets:
Assets measured at fair value	0.025
Other asset-backed securities | Level 3 | Comparability Adjustment | Discounted Cash Flows | Minimum
Assets:
Assets measured at fair value	0
Other asset-backed securities | Level 3 | Comparability Adjustment | Discounted Cash Flows | Maximum
Assets:
Assets measured at fair value	0.05
Other asset-backed securities | Level 3 | Comparability Adjustment | Discounted Cash Flows | Weighted Average
Assets:
Assets measured at fair value	0.025

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