Income Taxes Income Taxes - Additional Information (Details) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Income tax expense	$ (2,654)	$ (2,251)
Effective tax rate	16.30%	9.30%
Benefit related to share-based compensation tax deductions		$ 3,100
Valuation allowance for deferred tax assets	$ 42,400			$ 42,500
Increase (decrease) in valuation allowance	(100)	(200)
Unrecognized tax benefits	30,100			29,600
Increase (decrease) in uncertain tax positions	$ 500	$ 800
Transition tax on accumulated foreign earnings, percent					15.50%
Transition tax on accumulated foreign earnings, remaining earnings, percent					8.00%
Transition tax for accumulated foreign earnings, provisional liability					$ 15,700
Change in tax rate, deferred tax asset, income tax expense (benefit)				95,000
Federal Tax Administration (FTA)
Operating Loss Carryforwards [Line Items]
Change in tax rate, deferred tax asset, income tax expense (benefit)				$ 68,900
Scenario, Forecast
Operating Loss Carryforwards [Line Items]
Release of valuation allowance			$ 22,300