Securities Securities - Premium Amortization and Discount Accretion Included in Income on Securities (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Premium amortization	$ (31,540)	$ (29,511)	$ (94,873)	$ (88,798)
Discount accretion	637	1,274	1,793	3,835
Net (premium amortization) discount accretion	$ (30,903)	$ (28,237)	$ (93,080)	$ (84,963)

Amount of accretion of purchase discount on nonoperating securities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

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Amount of amortization of purchase premium on nonoperating securities.

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Amount of accretion (amortization) of purchase discount (premium) on nonoperating securities.

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