Marketable Securities - Fair Value of and Gross Unrealized Losses on Investment Securities (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2024 USD ($) position	Dec. 31, 2023 USD ($)
Marketable securities available-for-sale
Less than 12 months - Fair value	$ 264,119	$ 20,729
Less than 12 months - Unrealized loss	(1,237)	(323)
12 months or more - Fair value	1,363,076	1,704,010
12 months or more - Unrealized loss	(293,326)	(311,878)
Total - Fair value	1,627,195	1,724,739
Total - Unrealized loss	$ (294,563)	(312,201)
Number of investment positions with unrealized losses | position	387
U.S. government-sponsored enterprises
Marketable securities available-for-sale
Less than 12 months - Fair value	$ 0	0
Less than 12 months - Unrealized loss	0	0
12 months or more - Fair value	145,120	206,569
12 months or more - Unrealized loss	(26,787)	(33,644)
Total - Fair value	145,120	206,569
Total - Unrealized loss	(26,787)	(33,644)
Corporate debt issues
Marketable securities available-for-sale
Less than 12 months - Fair value	2,395	0
Less than 12 months - Unrealized loss	(38)	0
12 months or more - Fair value	7,619	7,688
12 months or more - Unrealized loss	(848)	(778)
Total - Fair value	10,014	7,688
Total - Unrealized loss	(886)	(778)
Municipal securities
Marketable securities available-for-sale
Less than 12 months - Fair value	13,977	2,753
Less than 12 months - Unrealized loss	(140)	(81)
12 months or more - Fair value	39,354	66,046
12 months or more - Unrealized loss	(10,054)	(10,363)
Total - Fair value	53,331	68,799
Total - Unrealized loss	(10,194)	(10,444)
Mortgage-backed securities
Marketable securities available-for-sale
Less than 12 months - Fair value	247,747	17,976
Less than 12 months - Unrealized loss	(1,059)	(242)
12 months or more - Fair value	1,170,983	1,423,707
12 months or more - Unrealized loss	(255,637)	(267,093)
Total - Fair value	1,418,730	1,441,683
Total - Unrealized loss	$ (256,696)	$ (267,335)