Derivative Financial Instruments - Schedule of Effect of Derivative Instruments on Statements of Financial Performance (Details) - Derivatives Designated as Hedges - Cash Flow Hedges - FX Forward Contracts - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain recognized in other comprehensive income	$ 232	$ 376
Revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) reclassified from accumulated other comprehensive income (loss) into earnings: effective portion	(11)	(4)
Cost of operations
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) reclassified from accumulated other comprehensive income (loss) into earnings: effective portion	$ 120	$ 54