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Employee Benefits - Pension Plan Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value Measurements, Recurring - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | $ 87,613 | $ 84,585
Cash and Cash Equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 3,336 | 3,371
Fixed Income |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 27,279 | 27,054
Equity Index Mutual Funds-International |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 3,362 | 3,421
Domestic Individual Equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 53,636 | 50,739
Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 84,277 | 81,214
Level 1 | Cash and Cash Equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 0 | 0
Level 1 | Fixed Income |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 27,279 | 27,054
Level 1 | Equity Index Mutual Funds-International |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 3,362 | 3,421
Level 1 | Domestic Individual Equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 53,636 | 50,739
Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 3,336 | 3,371
Level 2 | Cash and Cash Equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 3,336 | 3,371
Level 2 | Fixed Income |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 0 | 0
Level 2 | Equity Index Mutual Funds-International |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 0 | 0
Level 2 | Domestic Individual Equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 0 | 0
Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 0 | 0
Level 3 | Cash and Cash Equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 0 | 0
Level 3 | Fixed Income |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 0 | 0
Level 3 | Equity Index Mutual Funds-International |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | 0 | 0
Level 3 | Domestic Individual Equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pension plan assets measured at fair value | $ 0 | $ 0

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