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Summary of Significant Accounting Policies (Details) $ / shares in Units, $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 USD ($) plan $ / shares | Dec. 31, 2016 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Number of compensation plans | plan | 2 |
Award vesting period (in years) | 4 years |
ESPP, market price discount percentage | 5.00% |
Available-for-Sale | $ 300,200 | $ 346,996
Available-For-Sale Securities, at Amortized Cost | 301,876 | 347,615
Operating leases, future minimum payments due, future minimum sublease rentals | 2,200 |
Accounting Standards Update 2016-09 [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
New accounting pronouncement, effect of change on net income | $ 148 |
New accounting pronouncement, effect of change on basic earnings per share | $ / shares | $ 0.01 |
Accounting Standards Update 2018-02 [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Cumulative effect on retained earnings | $ (1,600) |
Adjustments to additional paid in capital, income tax rate reduction | 1,600 |
Accounting Standards Update 2014-09 [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Cumulative effect on retained earnings | 330 |
Fair Value, Measurements, Recurring [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Available-for-Sale | 300,200 | 346,996
Equity Securities [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Available-for-Sale | 1,561 | 1,382
Available-For-Sale Securities, at Amortized Cost | 1,120 | 1,120
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Available-for-Sale | $ 1,561 | $ 1,382
Minimum [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Intangible asset, useful life (in years) | 10 years |
Maximum [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Intangible asset, useful life (in years) | 15 years |
Building and Building Improvements [Member] | Minimum [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Property, Plant and Equipment, Useful Life | 20 years |
Building and Building Improvements [Member] | Maximum [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Property, Plant and Equipment, Useful Life | 40 years |
Furniture and Fixtures [Member] | Minimum [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Property, Plant and Equipment, Useful Life | 7 years |
Furniture and Fixtures [Member] | Maximum [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Property, Plant and Equipment, Useful Life | 10 years |
Computer Equipment [Member] | Minimum [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Property, Plant and Equipment, Useful Life | 5 years |
Computer Equipment [Member] | Maximum [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Property, Plant and Equipment, Useful Life | 7 years |

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