Fair Value Measurements - Valuation of Financial Instruments That are Marked-to-Market on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Assets
Trading investments	$ 35,908	$ 16,923
Estimated Fair Value	2,072,309	1,996,634
Fair Value Measurements on a Recurring Basis
Assets
Trading investments	35,908	16,923
Estimated Fair Value	2,072,309	1,996,634
Derivative instruments	459	729
Total earning assets	2,108,676	2,014,286
Liabilities
Derivative instruments	(360)	(287)
Fair Value Measurements on a Recurring Basis \| Level 1
Assets
Trading investments	0	0
Estimated Fair Value	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
Estimated Fair Value	2,072,309	1,996,634
Derivative instruments	459	729
Total earning assets	2,072,768	1,997,363
Liabilities
Derivative instruments	(360)	(287)
Fair Value Measurements on a Recurring Basis \| Level 3
Assets
Trading investments	35,908	16,923
Estimated Fair Value	0	0
Derivative instruments	0	0
Total earning assets	35,908	16,923
Liabilities
Derivative instruments	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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