Income Taxes - Net Deferred Balances (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Taxes on Income and Uncertain Tax Positions [Abstract]
Deferred Tax Assets Net Noncurrent	$ 15,460	$ 24,382
Non-current deferred tax liabilities	9,653	12,008
Deferred Tax Assets, Net, Total	$ 5,807	$ 12,374