Fair Value Measurements - Valuation of Financial Instruments That are Marked-to-Market on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Assets:
Trading investments	$ 52,561	$ 55,903
Available-for-sale investments	2,315,978	2,342,089
Derivative instruments	$ 0	$ 405
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Other Assets	Other Assets
Liabilities:
Derivative instruments	$ (251)	$ 0
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Other liabilities	Other liabilities
Fair Value Measurements on a Recurring Basis
Assets:
Trading investments	$ 52,561	$ 55,903
Available-for-sale investments	2,315,978	2,342,089
Derivative instruments	17	972
Total earning assets	2,368,556	2,398,964
Liabilities:
Derivative instruments	(268)	(567)
Fair Value Measurements on a Recurring Basis | Level 1
Assets:
Trading investments	0	0
Available-for-sale investments	0	0
Derivative instruments	0	0
Total earning assets	0	0
Liabilities:
Derivative instruments	0	0
Fair Value Measurements on a Recurring Basis | Level 2
Assets:
Trading investments	0	0
Available-for-sale investments	2,315,978	2,342,089
Derivative instruments	17	972
Total earning assets	2,315,995	2,343,061
Liabilities:
Derivative instruments	(268)	(567)
Fair Value Measurements on a Recurring Basis | Level 3
Assets:
Trading investments	52,561	55,903
Available-for-sale investments	0	0
Derivative instruments	0	0
Total earning assets	52,561	55,903
Liabilities:
Derivative instruments	$ 0	$ 0