Fair Value Measurements - Reconciliation of Beginning and Ending Balance of Level 3 Assets and Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Acquisition earnout accruals, beginning balance	$ (10,991)
Acquisition earnout accruals, ending balance	(7,213)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Acquisition earnout accruals, beginning balance	(10,991)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Business Combination, Acquisition Earnout Adjustment, Fair Value	705
Earnout accretion	(1,038)
Earnout payments	4,557
Foreign currency translation	(446)
Acquisition earnout accruals, ending balance	$ (7,213)