Fair Value Measurements - Valuation of Financial Instruments that are Marked-to-Market on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Assets:
Trading investments	$ 53,262	$ 54,481
Available-for-sale investments	1,933,226	2,411,622
Derivative instruments	$ 0	$ 0
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Other assets	Other assets
Liabilities:
Derivative instruments	$ (40)	$ (370)
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Other liabilities	Other liabilities
Fair Value Measurements Recurring
Assets:
Trading investments	$ 53,262	$ 54,481
Available-for-sale investments	1,933,226	2,411,622
Derivative instruments	0	0
Total	1,986,488	2,466,103
Liabilities:
Derivative instruments	(40)	(370)
Fair Value Measurements Recurring | Level 1
Assets:
Trading investments	0	0
Available-for-sale investments	0	0
Derivative instruments	0	0
Total	0	0
Liabilities:
Derivative instruments	0	0
Fair Value Measurements Recurring | Level 2
Assets:
Trading investments	0	0
Available-for-sale investments	1,930,537	2,411,622
Derivative instruments	0	0
Total	1,930,537	2,411,622
Liabilities:
Derivative instruments	(40)	(370)
Fair Value Measurements Recurring | Level 3
Assets:
Trading investments	53,262	54,481
Available-for-sale investments	2,689	0
Derivative instruments	0	0
Total	55,951	54,481
Liabilities:
Derivative instruments	$ 0	$ 0