Marketable Securities - Fair Value of and Gross Unrealized Losses on Investment Securities (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2025 USD ($) position	Dec. 31, 2024 USD ($)
Marketable securities available-for-sale
Less than 12 months - Fair value	$ 57,888	$ 313,235
Less than 12 months - Unrealized loss	(354)	(3,764)
12 months or more - Fair value	1,334,242	1,310,418
12 months or more - Unrealized loss	(226,038)	(279,793)
Total - Fair value	1,392,130	1,623,653
Total - Unrealized loss	$ (226,392)	(283,557)
Number of investment positions with unrealized losses | position	311
U.S. government-sponsored enterprises
Marketable securities available-for-sale
Less than 12 months - Fair value	$ 1,147	0
Less than 12 months - Unrealized loss	(18)	0
12 months or more - Fair value	149,315	145,507
12 months or more - Unrealized loss	(17,800)	(24,366)
Total - Fair value	150,462	145,507
Total - Unrealized loss	(17,818)	(24,366)
Municipal securities
Marketable securities available-for-sale
Less than 12 months - Fair value	4,861	15,407
Less than 12 months - Unrealized loss	(2)	(186)
12 months or more - Fair value	39,855	39,296
12 months or more - Unrealized loss	(9,247)	(10,012)
Total - Fair value	44,716	54,703
Total - Unrealized loss	(9,249)	(10,198)
Corporate debt issues
Marketable securities available-for-sale
Less than 12 months - Fair value	3,932	0
Less than 12 months - Unrealized loss	(42)	0
12 months or more - Fair value	3,450	8,335
12 months or more - Unrealized loss	(37)	(143)
Total - Fair value	7,382	8,335
Total - Unrealized loss	(79)	(143)
Mortgage-backed securities
Marketable securities available-for-sale
Less than 12 months - Fair value	47,948	297,828
Less than 12 months - Unrealized loss	(292)	(3,578)
12 months or more - Fair value	1,141,622	1,117,280
12 months or more - Unrealized loss	(198,954)	(245,272)
Total - Fair value	1,189,570	1,415,108
Total - Unrealized loss	$ (199,246)	$ (248,850)