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Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016
Change in Accounting Estimate [Line Items] |  |  |
Real Estate Acquired Through Foreclosure | [1] | $ 43,382 | $ 16,237
Deposit Bases |  |  |
Change in Accounting Estimate [Line Items] |  |  |
Intangible assets, amortization period |  | 10 years |
Minimum | Furniture and Fixtures |  |  |
Change in Accounting Estimate [Line Items] |  |  |
Useful life of premises and equipment |  | 3 years |
Minimum | Building |  |  |
Change in Accounting Estimate [Line Items] |  |  |
Useful life of premises and equipment |  | 7 years |
Maximum | Furniture and Fixtures |  |  |
Change in Accounting Estimate [Line Items] |  |  |
Useful life of premises and equipment |  | 15 years |
Maximum | Building |  |  |
Change in Accounting Estimate [Line Items] |  |  |
Useful life of premises and equipment |  | 45 years |
Non-Accruing | Minimum |  |  |
Change in Accounting Estimate [Line Items] |  |  |
Impaired commercial loans |  | $ 1,000 |
Undivided Profits |  |  |
Change in Accounting Estimate [Line Items] |  |  |
Adjustment to reflect adoption of ASU 2018-02 |  | 57,546 | $ (230)
Accumulated Other Comprehensive Income/(Loss) |  |  |
Change in Accounting Estimate [Line Items] |  |  |
Adjustment to reflect adoption of ASU 2018-02 | [2] | (57,546) |
Accounting Standards Update 2018-02 | Undivided Profits |  |  |
Change in Accounting Estimate [Line Items] |  |  |
Adjustment to reflect adoption of ASU 2018-02 |  | 57,500 |
Accounting Standards Update 2018-02 | Accumulated Other Comprehensive Income/(Loss) |  |  |
Change in Accounting Estimate [Line Items] |  |  |
Adjustment to reflect adoption of ASU 2018-02 |  | (57,500) |
Government Guaranteed Mortgage Loans upon Foreclosure Receivable |  |  |
Change in Accounting Estimate [Line Items] |  |  |
Real Estate Acquired Through Foreclosure |  | $ 3,800 |
[1] | December 31, 2017 and 2016 include $6.3 million and $8.1 million, respectively, of foreclosed residential real estate.
[2] | Due to the nature of the preferred stock issued by FHN and its subsidiaries, all components of Other comprehensive income/(loss) have been attributed solely to FHN as the controlling interest holder.

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