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Debt And Liquidity (Narrative) (Details) - USD ($) | Feb. 27, 2015 | Jun. 30, 2017 | Dec. 31, 2016 | Apr. 27, 2016 | Jul. 28, 2015 | Apr. 23, 2014 | Nov. 20, 2012
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Debt Instrument [Line Items] |  |  |  |  |  |  |
Fair value of debt |  | $ 363,900,000 |  |  |  |  |
Long-term Debt |  | 375,963,000 | $ 365,432,000 |  |  |  |
Minimum Liquidity |  |  |  | $ 25,000,000 |  |  |
Outstanding letters of credit |  | 14,100,000 |  |  |  |  |
Term Loan Balance |  | 29,500,000 |  |  |  |  |
Revolving Credit Facility Balance |  | $ 68,500,000 |  |  |  |  |
Stated interest rate |  | 6.375% |  |  |  |  |
Loan balance, net of unamortized discount |  | $ 8,007,000 | 8,852,000 |  |  |  |
12 Month Trailing EBITDA |  |  | 75,000,000 |  |  |  |
12 Month Trailing EBITDA Minimum (Low End) |  |  |  | 40,000,000 |  |  |
12 Month Trailing EBITDA Minimum (High End) |  |  |  | 35,000,000 |  |  |
Senior Notes |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Long-term Debt |  | 277,341,000 | $ 274,132,000 |  |  |  |
Principal amount issued |  |  |  |  |  |  | $ 300,000,000
Stated interest rate |  |  |  |  |  |  | 6.375%
Redemption price, percentage of principal, prior to November 15, 2016 |  |  |  |  |  |  | 100.00%
Repurchase price, percentage of principal, due to change in control |  |  |  |  |  |  | 101.00%
Minimum | Senior Notes |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Unpaid indebtedness or accelerated proceeds exceeds |  | 50,000,000 |  |  |  |  |
Unpaid judgment or decree in excess of |  | $ 50,000,000 |  |  |  |  |
Amended and Restated Credit Agreement | Minimum |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Undrawn commitment fee | 0.35% |  |  |  |  |  |
Amended and Restated Credit Agreement | Maximum |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Undrawn commitment fee | 0.70% |  |  |  |  |  |
Amended and Restated Credit Agreement | LIBOR | Minimum |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Margin spread on variable interest rate | 2.25% |  |  |  |  |  |
Amended and Restated Credit Agreement | LIBOR | Maximum |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Margin spread on variable interest rate | 4.75% |  |  |  |  |  |
Amended and Restated Credit Agreement | Revolving Credit Facility |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Borrowing capacity |  |  |  |  |  | $ 400,000,000 |
Amended and Restated Credit Agreement | Term Loan Facility |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Borrowing capacity | $ 40,000,000 |  |  |  |  |  |
Amended and Restated Credit Agreement July 2015 [Member] | Revolving Credit Facility |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Borrowing capacity |  |  |  | $ 225,000,000 | $ 375,000,000 |  |
Amended and Restated Credit Agreement July 2015 [Member] | Term Loan Facility |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Borrowing capacity |  |  |  |  | $ 40,000,000 |  |

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