XML 61 R46.htm IDEA: XBRL DOCUMENT
v3.24.3

Fair Value Accounting - Schedule of Assets and Liabilities Measured at Estimated Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands | Sep. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Assets |  |
Investment securities available for sale | $ 7,554,168 | $ 9,788,662
Mortgage loans held for sale | 36,943 | 47,338
U.S. Treasury securities |  |
Assets |  |
Investment securities available for sale | 1,214,363 | 597,629
Collateralized mortgage obligations issued by U.S. Government sponsored enterprises |  |
Assets |  |
Investment securities available for sale | 585,388 | 587,595
Mortgage-backed securities issued by U.S. Government agencies |  |
Assets |  |
Investment securities available for sale | 1,525,091 | 925,664
Mortgage-backed securities issued by U.S. Government sponsored enterprises |  |
Assets |  |
Investment securities available for sale | 2,069,369 | 6,430,379
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises |  |
Assets |  |
Investment securities available for sale | 2,121,613 | 1,209,783
Corporate debt securities and other debt securities |  |
Assets |  |
Investment securities available for sale | 8,731 | 8,672
Level 1 |  |
Assets |  |
Trading securities | 154 | 0
Investment securities available for sale | 1,214,363 | 597,629
Other investments | 0 | 0
Mutual funds and mutual funds held in rabbi trusts | 62,901 | 53,742
Derivative assets | 0 | 0
Liabilities |  |
Securities sold short |  | 3,496
Mutual funds held in rabbi trusts | 47,484 | 38,735
Derivative liabilities | 0 | 0
Level 2 |  |
Assets |  |
Trading securities | 13,719 | 12,898
Investment securities available for sale | 6,339,805 | 9,191,033
Other investments | 0 | 0
Mutual funds and mutual funds held in rabbi trusts | 0 | 0
Derivative assets | 84,673 | 94,903
Liabilities |  |
Securities sold short |  | 0
Mutual funds held in rabbi trusts | 0 | 0
Derivative liabilities | 175,413 | 259,650
Level 3 |  |
Assets |  |
Trading securities | 0 | 0
Investment securities available for sale | 0 | 0
Other investments | 14,711 | 12,560
Mutual funds and mutual funds held in rabbi trusts | 0 | 0
Derivative assets | 0 | 0
Liabilities |  |
Securities sold short |  | 0
Mutual funds held in rabbi trusts | 0 | 0
Derivative liabilities | 0 | 0
Fair Value, Measurements, Recurring Basis |  |
Assets |  |
Trading securities | 13,873 | 12,898
Investment securities available for sale | 7,554,168 | 9,788,662
Mortgage loans held for sale | 36,943 | 47,338
Other investments | 14,711 | 12,560
Mutual funds and mutual funds held in rabbi trusts | 62,901 | 53,742
Derivative assets | 84,673 | 94,903
Liabilities |  |
Securities sold short | 0 | 3,496
Mutual funds held in rabbi trusts | 47,484 | 38,735
Derivative liabilities | 175,413 | 259,650
Fair Value, Measurements, Recurring Basis | U.S. Treasury securities |  |
Assets |  |
Trading securities | 154 | 0
Investment securities available for sale | 1,214,363 | 597,629
Fair Value, Measurements, Recurring Basis | Collateralized mortgage obligations issued by U.S. Government sponsored enterprises |  |
Assets |  |
Trading securities | 0 | 2,910
Investment securities available for sale | 585,388 | 587,595
Fair Value, Measurements, Recurring Basis | Other mortgage-backed securities |  |
Assets |  |
Trading securities | 0 | 2,149
Fair Value, Measurements, Recurring Basis | Asset-backed securities |  |
Assets |  |
Trading securities | 13,719 | 7,839
Fair Value, Measurements, Recurring Basis | U.S. Government agency securities |  |
Assets |  |
Investment securities available for sale | 29,613 | 28,940
Fair Value, Measurements, Recurring Basis | Mortgage-backed securities issued by U.S. Government agencies |  |
Assets |  |
Investment securities available for sale | 1,525,091 | 925,664
Fair Value, Measurements, Recurring Basis | Mortgage-backed securities issued by U.S. Government sponsored enterprises |  |
Assets |  |
Investment securities available for sale | 2,069,369 | 6,430,379
Fair Value, Measurements, Recurring Basis | Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises |  |
Assets |  |
Investment securities available for sale | 2,121,613 | 1,209,783
Fair Value, Measurements, Recurring Basis | Corporate debt securities and other debt securities |  |
Assets |  |
Investment securities available for sale | 8,731 | 8,672
Fair Value, Measurements, Recurring Basis | Level 1 |  |
Assets |  |
Trading securities | 154 | 0
Investment securities available for sale | 1,214,363 | 597,629
Mortgage loans held for sale | 0 | 0
Other investments | 0 | 0
Mutual funds and mutual funds held in rabbi trusts | 62,901 | 53,742
Derivative assets | 0 | 0
Liabilities |  |
Securities sold short | 0 | 3,496
Mutual funds held in rabbi trusts | 47,484 | 38,735
Derivative liabilities | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 1 | U.S. Treasury securities |  |
Assets |  |
Trading securities | 154 | 0
Investment securities available for sale | 1,214,363 | 597,629
Fair Value, Measurements, Recurring Basis | Level 1 | Collateralized mortgage obligations issued by U.S. Government sponsored enterprises |  |
Assets |  |
Trading securities | 0 | 0
Investment securities available for sale | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 1 | Other mortgage-backed securities |  |
Assets |  |
Trading securities | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 1 | Asset-backed securities |  |
Assets |  |
Trading securities | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 1 | U.S. Government agency securities |  |
Assets |  |
Investment securities available for sale | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 1 | Mortgage-backed securities issued by U.S. Government agencies |  |
Assets |  |
Investment securities available for sale | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 1 | Mortgage-backed securities issued by U.S. Government sponsored enterprises |  |
Assets |  |
Investment securities available for sale | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 1 | Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises |  |
Assets |  |
Investment securities available for sale | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 1 | Corporate debt securities and other debt securities |  |
Assets |  |
Investment securities available for sale | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 2 |  |
Assets |  |
Trading securities | 13,719 | 12,898
Investment securities available for sale | 6,339,805 | 9,191,033
Mortgage loans held for sale | 36,943 | 47,338
Other investments | 0 | 0
Mutual funds and mutual funds held in rabbi trusts | 0 | 0
Derivative assets | 84,673 | 94,903
Liabilities |  |
Securities sold short | 0 | 0
Mutual funds held in rabbi trusts | 0 | 0
Derivative liabilities | 175,413 | 259,650
Fair Value, Measurements, Recurring Basis | Level 2 | U.S. Treasury securities |  |
Assets |  |
Trading securities | 0 | 0
Investment securities available for sale | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 2 | Collateralized mortgage obligations issued by U.S. Government sponsored enterprises |  |
Assets |  |
Trading securities | 0 | 2,910
Investment securities available for sale | 585,388 | 587,595
Fair Value, Measurements, Recurring Basis | Level 2 | Other mortgage-backed securities |  |
Assets |  |
Trading securities | 0 | 2,149
Fair Value, Measurements, Recurring Basis | Level 2 | Asset-backed securities |  |
Assets |  |
Trading securities | 13,719 | 7,839
Fair Value, Measurements, Recurring Basis | Level 2 | U.S. Government agency securities |  |
Assets |  |
Investment securities available for sale | 29,613 | 28,940
Fair Value, Measurements, Recurring Basis | Level 2 | Mortgage-backed securities issued by U.S. Government agencies |  |
Assets |  |
Investment securities available for sale | 1,525,091 | 925,664
Fair Value, Measurements, Recurring Basis | Level 2 | Mortgage-backed securities issued by U.S. Government sponsored enterprises |  |
Assets |  |
Investment securities available for sale | 2,069,369 | 6,430,379
Fair Value, Measurements, Recurring Basis | Level 2 | Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises |  |
Assets |  |
Investment securities available for sale | 2,121,613 | 1,209,783
Fair Value, Measurements, Recurring Basis | Level 2 | Corporate debt securities and other debt securities |  |
Assets |  |
Investment securities available for sale | 8,731 | 8,672
Fair Value, Measurements, Recurring Basis | Level 3 |  |
Assets |  |
Trading securities | 0 | 0
Investment securities available for sale | 0 | 0
Mortgage loans held for sale | 0 | 0
Other investments | 14,711 | 12,560
Mutual funds and mutual funds held in rabbi trusts | 0 | 0
Derivative assets | 0 | 0
Liabilities |  |
Securities sold short | 0 | 0
Mutual funds held in rabbi trusts | 0 | 0
Derivative liabilities | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 3 | U.S. Treasury securities |  |
Assets |  |
Trading securities | 0 | 0
Investment securities available for sale | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 3 | Collateralized mortgage obligations issued by U.S. Government sponsored enterprises |  |
Assets |  |
Trading securities | 0 | 0
Investment securities available for sale | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 3 | Other mortgage-backed securities |  |
Assets |  |
Trading securities | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 3 | Asset-backed securities |  |
Assets |  |
Trading securities | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 3 | U.S. Government agency securities |  |
Assets |  |
Investment securities available for sale | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 3 | Mortgage-backed securities issued by U.S. Government agencies |  |
Assets |  |
Investment securities available for sale | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 3 | Mortgage-backed securities issued by U.S. Government sponsored enterprises |  |
Assets |  |
Investment securities available for sale | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 3 | Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises |  |
Assets |  |
Investment securities available for sale | 0 | 0
Fair Value, Measurements, Recurring Basis | Level 3 | Corporate debt securities and other debt securities |  |
Assets |  |
Investment securities available for sale | $ 0 | $ 0

X
- Definition Mutual Funds And Mutual Funds Held In Rabbi Trusts In Assets + References No definition available. + Details
Name: | syn_MutualFundsAndMutualFundsHeldInRabbiTrustsInAssets
Namespace Prefix: | syn_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Mutual Funds And Mutual Funds Held In Rabbi Trusts In Liability + References No definition available. + Details
Name: | syn_MutualFundsAndMutualFundsHeldInRabbiTrustsInLiability
Namespace Prefix: | syn_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479130/326-30-45-1 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 103 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-103 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 100 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-100 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(2)(i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-3 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 12 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478795/946-210-50-12 Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478795/946-210-50-6 Reference 11: http://www.xbrl.org/2003/role/exampleRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 55 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477439/946-210-55-1 Reference 12: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478795/946-210-50-6 Reference 13: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478795/946-210-50-6 Reference 14: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(4) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478795/946-210-50-6 Reference 15: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478795/946-210-50-1 Reference 16: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478795/946-210-50-1 Reference 17: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478795/946-210-50-1 Reference 18: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478795/946-210-50-1 Reference 19: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478795/946-210-50-6 Reference 20: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478795/946-210-50-6 Reference 21: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-04(3)(c)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479170/946-210-S99-1 Reference 22: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 5C -Subparagraph (SX 210.12-13C(Column H)(Footnote 7)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5C Reference 23: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-04(3)(b)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479170/946-210-S99-1 Reference 24: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 5 -Subparagraph (SX 210.12-13(Column A)(Footnote 3)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5 Reference 25: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 5C -Subparagraph (SX 210.12-13C(Column H)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5C Reference 26: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 5A -Subparagraph (SX 210.12-13A(Column E)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5A Reference 27: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 5B -Subparagraph (SX 210.12-13B(Column E)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5B Reference 28: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 5B -Subparagraph (SX 210.12-13B(Column E)(Footnote 4)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5B Reference 29: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483466/210-20-50-3 Reference 30: http://www.xbrl.org/2003/role/exampleRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 22 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483444/210-20-55-22 Reference 31: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483444/210-20-55-10 Reference 32: http://www.xbrl.org/2003/role/disclosureRef -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482907/825-10-50-10 + Details
Name: | us-gaap_DerivativeAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair value, before effects of master netting arrangements, of a financial liability or 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 liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4B -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4B -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 22 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483444/210-20-55-22 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483466/210-20-50-3 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483444/210-20-55-7 Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 4D -Subparagraph (c)(2) -SubTopic 20 -Topic 860 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481326/860-20-50-4D + Details
Name: | us-gaap_DerivativeFairValueOfDerivativeLiability
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value portion of mortgage loans held-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
Name: | us-gaap_MortgagesHeldForSaleFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investments classified as other. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(12)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(3)(a)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1 + Details
Name: | us-gaap_OtherInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair value portion of liabilities pertaining to principal and customer trading transactions, or which may be incurred with the objective of generating a profit from short-term fluctuations in price as part of an entity's market-making, hedging and proprietary trading. Examples include, but are not limited to, short positions in securities, derivatives and commodities. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
Name: | us-gaap_TradingLiabilitiesFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(4)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483467/210-10-45-1 + Details
Name: | us-gaap_TradingSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=syn_CollateralizedMortgageObligationsIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=syn_MortgageBackedSecuritiesIssuedByUSGovernmentAgenciesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=syn_CommercialMortgageBackedSecuritiesIssuedByUSGovernmentSponsoredAgenciesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesOtherMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |