Securities Securities - Premium Amortization and Discount Accretion Included in Income on Securities (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Premium amortization	$ (29,408)	$ (26,689)	$ (59,287)	$ (52,723)
Discount accretion	1,378	2,010	2,561	3,787
Net (premium amortization) discount accretion	$ (28,030)	$ (24,679)	$ (56,726)	$ (48,936)

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=115205541&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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