Fair Value Measurement Fair Value Measurements, Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Current	$ 17,214	$ 37,329	[1]
Available for sale securities, noncurrent	2,021	2,025	[1]
Available-for-sale Securities		40,086
Assets, Fair Value Disclosure	20,822
Prepaid Expenses and Other Current Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	874	187
Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	713	545
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Current	0	0
Available for sale securities, noncurrent	0	0
Available-for-sale Securities		0
Assets, Fair Value Disclosure	0
Fair Value, Inputs, Level 1 [Member] | Prepaid Expenses and Other Current Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 1 [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Current	17,214	37,329
Available for sale securities, noncurrent	2,021	2,025
Available-for-sale Securities		40,086
Assets, Fair Value Disclosure	20,822
Fair Value, Inputs, Level 2 [Member] | Prepaid Expenses and Other Current Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	874	187
Fair Value, Inputs, Level 2 [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	713	545
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Current	0	0
Available for sale securities, noncurrent	0	0
Available-for-sale Securities		0
Assets, Fair Value Disclosure	0
Fair Value, Inputs, Level 3 [Member] | Prepaid Expenses and Other Current Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 3 [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	0	0
Earn-out liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonfinancial Liabilities Fair Value Disclosure	39,700	47,400
Earn-out liability [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonfinancial Liabilities Fair Value Disclosure	0	0
Earn-out liability [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonfinancial Liabilities Fair Value Disclosure	0	0
Earn-out liability [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonfinancial Liabilities Fair Value Disclosure	39,700	47,400
Liabilities, Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonfinancial Liabilities Fair Value Disclosure	39,700	47,400
Liabilities, Total [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonfinancial Liabilities Fair Value Disclosure	0	0
Liabilities, Total [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonfinancial Liabilities Fair Value Disclosure	0	0
Liabilities, Total [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonfinancial Liabilities Fair Value Disclosure	$ 39,700	$ 47,400

[1] December 31, 2018 balances were derived from audited consolidated financial statements.