v3.8.0.1

Summary of Significant Accounting Policies - Additional Information (Details) |  | 12 Months Ended |
--- | --- | --- | ---
Jan. 18, 2017 | Dec. 31, 2017 USD ($) Employees Subsidiary Clients | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Jan. 04, 2017 shares
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Number of inactive wholly owned subsidiaries | Subsidiary |  | 2 |  |  |  |
Number of full-time equivalent employees | Employees |  | 394 |  |  |  |
Cash and cash equivalents held at the Federal Reserve Bank |  | $ 101,900,000 |  |  |  |
Impaired long-lived assets |  | 0 | $ 0 |  |  |
Investment in FHLB stock |  | 19,060,000 | 33,750,000 |  |  |
Impairment charges |  | 0 | 0 |  |  |
Core deposit intangible amortization expense |  | 394,000 | 239,000 | $ 180,000 |  |
Stock split, conversion ratio | 2.00 |  |  |  |  |
Additional share of common stock following stock split | shares |  |  |  |  |  | 1
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to retained earnings |  | 900,000 |  |  |  |
Core Deposit |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Core deposit intangible assets |  |  | 6,300,000 | 900,000 |  |
Core deposit intangible amortization expense |  |  | $ 400,000 | $ 200,000 | $ 200,000 |
Federal Home Loan Bank Stock |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Adjustments in carrying value |  | $ 0 |  |  |  |
Minimum |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Estimated useful lives |  | 3 years |  |  |  |
Estimated useful lives of other intangible assets |  | 7 years |  |  |  |
Maximum |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Estimated useful lives |  | 10 years |  |  |  |
Estimated useful lives of other intangible assets |  | 10 years |  |  |  |
FFA |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Approximate number of clients | Clients |  | 1,500 |  |  |  |
Aggregate assets under management |  | $ 4,300,000,000 |  |  |  |

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