Income Taxes - Valuation Allowance and Tax Reforms (Details) - USD ($) $ in Thousands		12 Months Ended		24 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017
Valuation Allowance
Increase in valuation allowance		$ 17,504	$ 9,060
Tax Reforms
Transition tax on foreign earnings related to cash and cash equivalents, Percent		15.50%
Transition tax on foreign earnings related to other assets, Percent		8.00%
Federal statutory income tax rate		34.00%	34.00%
TCJ Act 2017, Change in tax rate, reduction in deferred tax asset, provisional income tax expense		$ 11,300
Uncertain Tax Positions
Interest and penalties pertaining to uncertain tax positions		$ 0	$ 0	$ 0
Forecast
Tax Reforms
Federal statutory income tax rate	21.00%