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Restructuring - Narrative (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Jan. 31, 2018 | Jun. 21, 2017
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Expected number of positions eliminated (as a percent) | 50.00% |  | 50.00% |  |  |  |  |  | 50.00%
Restructuring | $ 2,892 | $ 1,992 | $ 3,584 | $ 3,480 | $ 4,030 | $ 5,400 | $ 0 |  |
Payments for restructuring |  |  | 1,311 |  | 6,551 |  |  |  |
Restructuring reserve | 500 |  | 500 |  | 400 |  |  |  |
Restructuring cost incurred to date | 12,800 |  | 12,800 |  | 9,400 |  |  |  |
One-time Termination Benefits |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring |  | 1,300 |  | 2,300 | 2,700 |  |  |  |
Special Termination Benefits |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring |  | 300 |  | 300 | 300 |  |  |  |
Fixed Asset Impairment |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring |  | 300 |  | 300 | 400 |  |  |  |
Legal Fees |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring |  | $ 100 |  |  | 600 |  |  |  |
May 2018 Restructuring Activities |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring cost incurred to date | 2,900 |  | 2,900 |  |  |  |  |  |
May 2018 Restructuring Activities | One-time Termination Benefits |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring | 700 |  |  |  |  |  |  |  |
May 2018 Restructuring Activities | Fixed Asset Impairment |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring | 2,200 |  | 2,200 |  |  |  |  |  |
January 2018 and May 2018 Restructuring Activities | One-time Termination Benefits |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring |  |  | 1,400 |  |  |  |  |  |
Payments for restructuring |  |  | 1,300 |  |  |  |  |  |
December 2016 Restructuring Activities |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Expected number of positions eliminated (as a percent) |  |  |  |  |  | 30.00% |  |  |
Restructuring |  |  |  |  | 6,900 |  |  |  |
Payments for restructuring |  |  |  |  | 4,700 |  |  |  |
Restructuring cost incurred to date | 6,900 |  | 6,900 |  | 6,900 |  |  |  |
December 2016 Restructuring Activities | One-time Termination Benefits |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring |  |  |  |  | 2,400 |  |  |  |
Payments for restructuring |  |  |  | $ 4,100 |  |  |  |  |
Restructuring cost incurred to date |  |  |  |  | 2,400 |  |  |  |
December 2016 Restructuring Activities | Special Termination Benefits |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring |  |  |  |  | 1,700 |  |  |  |
Restructuring cost incurred to date |  |  |  |  | 1,700 |  |  |  |
December 2016 Restructuring Activities | Fixed Asset Impairment |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring |  |  |  |  | 2,000 |  |  |  |
Restructuring cost incurred to date |  |  |  |  | 2,000 |  |  |  |
December 2016 Restructuring Activities | Legal Fees |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring |  |  |  |  | 900 |  |  |  |
Restructuring cost incurred to date |  |  |  |  | 900 |  |  |  |
June 2017 Restructuring Activities |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Expected number of positions eliminated (as a percent) |  |  |  |  |  |  |  |  | 50.00%
Restructuring |  |  |  |  | 2,300 |  |  |  |
Payments for restructuring |  |  |  |  | 1,900 |  |  |  |
Restructuring cost incurred to date | 2,300 |  | 2,300 |  | 2,300 |  |  |  |
June 2017 Restructuring Activities | One-time Termination Benefits |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring |  |  |  |  | 1,700 |  |  |  |
June 2017 Restructuring Activities | Special Termination Benefits |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring |  |  |  |  | 300 |  |  |  |
June 2017 Restructuring Activities | Fixed Asset Impairment |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring |  |  |  |  | 200 |  |  |  |
June 2017 Restructuring Activities | Legal Fees |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring |  |  |  |  | $ 100 |  |  |  |
January 2018 Restructuring Activities |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Expected number of positions eliminated (as a percent) |  |  |  |  |  |  |  | 50.00% |
Restructuring cost incurred to date | $ 700 |  | $ 700 |  |  |  |  |  |

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