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Stockholders' Equity (Details) - USD ($) $ in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Jun. 13, 2016 | Jan. 16, 2015
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |
Stock Repurchase Program, Authorized Amount |  |  |  | $ 150,000 | $ 100,000
Stock Repurchased and Retired During Period, Shares |  |  | 43,000 |  |
Payments for Repurchase of Equity |  |  | $ (1,600) |  |
sharesreceivedforexercisepriceofoptions |  |  | 46,174 |  |
payment exercise of stock option |  |  | $ 2,200 |  |
Stock Repurchased and Retired During Period, Value | $ (58,070) | $ (43,091) | $ (3,819) |  |
Stock Issued During Period, Shares, Acquisitions |  |  | 794,700 |  |
Stock Issued During Period, Value, Acquisitions |  |  | $ 30,183 |  |
Stock Repurchase Program, Remaining Authorized Repurchase Amount | $ 48,800 |  |  |  |
Common Stock [Member] |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |
Stock Repurchased and Retired During Period, Shares | 1,229,249 | 1,133,553 | 89,174 |  |
Stock Repurchased and Retired During Period, Value | $ (12) | $ (11) | $ (1) |  |
Stock Issued During Period, Shares, Acquisitions |  |  | 794,700 |  |
Stock Issued During Period, Value, Acquisitions |  |  | $ 8 |  |
Additional Paid-in Capital [Member] |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |
Payments for Repurchase of Equity |  |  | (400) |  |
payment exercise of stock option |  |  | 800 |  |
Stock Repurchased and Retired During Period, Value | (13,229) | (11,885) | (1,173) |  |
Stock Issued During Period, Value, Acquisitions |  |  | 30,175 |  |
Retained Earnings [Member] |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |
Payments for Repurchase of Equity |  |  | (1,200) |  |
payment exercise of stock option |  |  | 1,400 |  |
Stock Repurchased and Retired During Period, Value | $ (44,829) | $ (31,195) | $ (2,645) |  |

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