Investment Information - Net realized gains and losses (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Net realized gains and losses:
Available for sale securities, gross gains on investment sales		$ 178,200	$ 43,365
Available for sale securities, gross losses on investment sales		(31,968)	(31,656)
Net realized gains (losses) on sales during the period		(539)	10,930
Net unrealized gains (losses) on equity securities still held at reporting date		(175,566)	37,136
Provision for credit losses		(9,349)
Allowance for credit losses - underwriting related		(3,270)	0
Net impairment losses		(533)	(1,309)
Derivative instruments	[1]	127,189	35,871
Other		(2,097)	(8,410)
Net realized gains (losses)		(366,960)	140,256
Fixed maturities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		(127,666)	31,148
Provision for credit losses		(9,320)	0
Other investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		(307,800)	18,195
Equity securities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		(4,909)	4,266
Short-term investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		$ (8,681)	$ 720

[1] See note 9 for information on the Company’s derivative instruments.