Fair Value Measurements - Valuation of Financial Instruments That are Marked-to-Market on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets
Trading investments	$ 30,594	$ 16,923
Estimated Fair Value	2,115,885	1,996,634
Fair Value Measurements on a Recurring Basis
Assets
Trading investments	30,594	16,923
Estimated Fair Value	2,115,885	1,996,634
Derivative instruments	1,054	729
Total earning assets	2,147,533	2,014,286
Liabilities
Derivative instruments	(451)	(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	2,115,885	1,996,634
Derivative instruments	1,054	729
Total earning assets	2,116,939	1,997,363
Liabilities
Derivative instruments	(451)	(287)
Fair Value Measurements on a Recurring Basis \| Level 3
Assets
Trading investments	30,594	16,923
Estimated Fair Value	0	0
Derivative instruments	0	0
Total earning assets	30,594	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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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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