Securities Sold Under Agreements to Repurchase - Carrying Value of Repurchase Agreements (Details) - Overnight and Continuous - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Securities Sold Under Agreements to Repurchase
Repurchase agreements	$ 996,878	$ 1,004,583
State and local governments
Securities Sold Under Agreements to Repurchase
Repurchase agreements	418,077	787,016
Corporate bonds
Securities Sold Under Agreements to Repurchase
Repurchase agreements	175,522	217,567
Residential mortgage-backed securities
Securities Sold Under Agreements to Repurchase
Repurchase agreements	391,505	0
Commercial mortgage-backed securities
Securities Sold Under Agreements to Repurchase
Repurchase agreements	$ 11,774	$ 0

Amount, before effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and elected not to be offset.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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