v3.8.0.1

Income Taxes - Change in Deferred Tax Valuation Allowance (Details) - Income tax valuation allowance - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Valuation allowance |  |  |
Balance at Beginning of Period | $ 62,297 | $ 54,739 | $ 44,309
Additions Charged to Expense | 17,967 | 7,558 | 10,430
Deductions | (9,163) |  |
Balance at End of Period | $ 71,101 | $ 62,297 | $ 54,739

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