Investments - Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net Investment Income [Line Items]
Investment expenses	$ (2,151)	$ (2,179)	$ (7,262)	$ (7,420)
Total net investment income	93,718	93,071	256,403	279,329
Investment Portfolio
Net Investment Income [Line Items]
Total net investment income	69,219	69,313	184,262	232,376
Deposit asset on reinsurance
Net Investment Income [Line Items]
Total net investment income	24,499	23,758	72,141	46,953
Fixed maturity securities
Net Investment Income [Line Items]
Net investment income - investment portfolio	56,420	59,319	174,727	227,196
Equity securities
Net Investment Income [Line Items]
Net investment income - investment portfolio	1,130	1,107	3,520	3,697
Limited partnership interests
Net Investment Income [Line Items]
Net investment income - investment portfolio	11,046	6,859	4,862	22,759
Short-term and other investments
Net Investment Income [Line Items]
Net investment income - investment portfolio	$ 2,774	$ 4,207	$ 8,415	$ (13,856)

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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