Investments in Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 1,178,048	$ 1,090,347
Fair Value
Debt Securities, Available-for-sale [Line Items]
Cost	1,011,221	949,332
Gross Unrealized, Gains	204,584	194,881
Gross Unrealized, Losses	(37,757)	(53,866)
Equity securities	1,178,048	1,090,347
Fair Value | Common stock
Debt Securities, Available-for-sale [Line Items]
Cost	671,958	664,997
Gross Unrealized, Gains	196,093	191,806
Gross Unrealized, Losses	(21,382)	(18,749)
Equity securities	846,669	838,054
Fair Value | Preferred stocks
Debt Securities, Available-for-sale [Line Items]
Cost	339,263	284,335
Gross Unrealized, Gains	8,491	3,075
Gross Unrealized, Losses	(16,375)	(35,117)
Equity securities	331,379	252,293
Carrying Value
Debt Securities, Available-for-sale [Line Items]
Equity securities	1,178,048	1,090,347
Carrying Value | Common stock
Debt Securities, Available-for-sale [Line Items]
Equity securities	846,669	838,054
Carrying Value | Preferred stocks
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 331,379	$ 252,293