Investments - Net Investment Income (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Investment fees and expenses	$ (6,484)	$ (6,681)	$ (6,977)
Net investment income	93,269	91,884	95,662
Fixed maturities
Debt Securities, Available-for-sale [Line Items]
Investment income	72,593	69,515	75,669
Equities
Debt Securities, Available-for-sale [Line Items]
Investment income	17,650	21,418	17,198
Short-term investments, including Other
Debt Securities, Available-for-sale [Line Items]
Investment income	7,493	5,649	7,793
BOLI
Debt Securities, Available-for-sale [Line Items]
Investment income	$ 2,017	$ 1,983	$ 1,979

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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