Summary of Significant Accounting Policies - Schedule of Amounts of Non-hedging Derivative Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Forward Purchase Contracts [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 0	$ 3
Liability Derivatives	413	4
Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives		3
Liability Derivatives	413	4
Derivatives Not Designated as Hedging Instruments [Member] | Forward Purchase Contracts [Member] | Prepaid Expenses and Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives		3
Derivatives Not Designated as Hedging Instruments [Member] | Forward Purchase Contracts [Member] | Accrued Liabilities Current [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 413	$ 4