Investments - Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Net Investment Income [Line Items]
Investment expenses	$ (2,886)	$ (2,688)	$ (5,111)	$ (5,241)
Total net investment income	80,410	93,458	162,685	186,258
Investment Portfolio
Net Investment Income [Line Items]
Total net investment income	56,456	70,263	115,043	163,063
Deposit asset on reinsurance
Net Investment Income [Line Items]
Total net investment income	23,954	23,195	47,642	23,195
Fixed maturity securities
Net Investment Income [Line Items]
Net investment income - investment portfolio	58,861	83,561	118,307	167,877
Equity securities
Net Investment Income [Line Items]
Net investment income - investment portfolio	1,182	1,392	2,390	2,590
Limited partnership interests
Net Investment Income [Line Items]
Net investment income - investment portfolio	(3,485)	9,449	(6,184)	15,900
Short-term and other investments
Net Investment Income [Line Items]
Net investment income - investment portfolio	$ 2,784	$ (21,451)	$ 5,641	$ (18,063)

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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