Fair Value Measurements - Changes to Fair Value of Earnout Liabilities (Details) - Recurring Measurement Basis - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Earnout consideration liability	$ 1,899	$ 1,396
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Earnout consideration liability	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Earnout consideration liability	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Earnout consideration liability	$ 1,899	$ 1,396