Fair Value Measurements - Summary of Changes in the Fair Value of the Contingent Consideration Liability (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Payment of contingent consideration	$ (897)	$ (816)
Fair value adjustment of contingent consideration	(938)	(92)
NLEX [Member] | Contingent Consideration [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning balance	2,733	3,457
Payment of contingent consideration	(897)	(816)
Fair value adjustment of contingent consideration	938	92
Ending balance	$ 2,774	$ 2,733