Fair Value Accounting (Changes In Fair Value Included In Consolidated Statements Of Income) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Mortgage loans held for sale	$ 115	$ 1,203
Fair value	50,439		$ 48,024
Unpaid principal balance	49,139		46,839
Fair value less aggregate unpaid principal balance	$ 1,300		$ 1,185

Changes in the fair value of mortgage loans held for sale that were included in the consolidated statements of income during the reporting period.

No definition available.

+ Details

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Namespace Prefix:	syn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair value option, aggregate unpaid principal balance of mortgage loans held for sale.

+ References

No definition available.

+ Details

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Namespace Prefix:	syn_
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- References

No definition available.

+ Details

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- Definition

This item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of long-term debt instruments that have contractual principal amounts and for which the fair value option has been elected.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

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Data Type:	xbrli:monetaryItemType
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- Definition

Amount, after allowance for bad debt, of mortgage loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

+ Details

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