Investments - Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Net Investment Income [Line Items]
Investment expenses	$ (2,225)	$ (2,553)
Total net investment income	82,275	92,800
Investment Portfolio
Net Investment Income [Line Items]
Total net investment income	58,587	92,800
Deposit asset on reinsurance
Net Investment Income [Line Items]
Total net investment income	23,688	0
Fixed maturity securities
Net Investment Income [Line Items]
Net investment income - investment portfolio	59,446	84,316
Equity securities
Net Investment Income [Line Items]
Net investment income - investment portfolio	1,208	1,198
Limited partnership interests
Net Investment Income [Line Items]
Net investment income - investment portfolio	(2,699)	6,451
Short-term and other investments
Net Investment Income [Line Items]
Net investment income - investment portfolio	$ 2,857	$ 3,388

Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein.

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