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Restructuring - Narrative (Details) - USD ($) $ in Thousands | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Jun. 21, 2017
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring costs incurred to date |  | $ 12,800 |  | $ 12,800 |  | $ 9,400 |  |  |
Decrease in number of employees (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 accrual |  | $ 500 |  | $ 500 |  | 400 |  |  |
Cash award |  |  |  |  |  | $ 800 |  |  |
Deferred compensation arrangement with individual, requisite service period (in months) |  |  |  |  |  | 18 months |  |  |
Options granted (in shares) |  | 1,179,877 | 2,183,106 |  | 4,015,356 | 4,386,856 |  |  |
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 |  |  |
Employee Stock Option |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Options granted (in shares) | 143,000 |  |  | 1,179,877 |  |  |  |  |
Vesting period (in years) | 2 years |  |  |  |  |  |  |  |
December 2016 Restructuring Activities |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Number of positions eliminated, percent |  |  |  |  |  |  | 30.00% |  |
Restructuring costs incurred to date |  | $ 6,900 |  | $ 6,900 |  | 6,900 |  |  |
Decrease in number of employees (percent) |  |  |  |  |  |  | 30.00% |  |
Restructuring |  |  |  |  |  | 6,900 |  |  |
Payments for restructuring |  |  |  |  |  | 4,700 |  |  |
December 2016 Restructuring Activities | One-time Termination Benefits |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring costs incurred to date |  |  |  |  |  | 2,400 |  |  |
Restructuring |  |  |  |  |  | 2,400 |  |  |
Payments for restructuring |  |  |  |  | $ 4,100 |  |  |  |
December 2016 Restructuring Activities | Special Termination Benefits |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring costs incurred to date |  |  |  |  |  | 1,700 |  |  |
Restructuring |  |  |  |  |  | 1,700 |  |  |
December 2016 Restructuring Activities | Fixed Asset Impairment |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring costs incurred to date |  |  |  |  |  | 2,000 |  |  |
Restructuring |  |  |  |  |  | 2,000 |  |  |
December 2016 Restructuring Activities | Legal Fees |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring costs incurred to date |  |  |  |  |  | 900 |  |  |
Restructuring |  |  |  |  |  | 900 |  |  |
June 2017 Restructuring Activities |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring costs incurred to date |  | $ 2,300 |  | $ 2,300 |  | 2,300 |  |  |
Decrease in number of employees (percent) |  |  |  |  |  |  |  |  | 50.00%
Restructuring |  |  |  |  |  | 2,300 |  |  |
Payments for restructuring |  |  |  |  |  | 1,900 |  |  |
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 Announcement |  |  |  |  |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |
Restructuring costs incurred to date |  |  |  |  |  | $ 200 |  |  |

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