Fair Value Measurements - Fair Value Measurement of Financial Assets and Liabilities on Recurring Basis (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
NLEX [Member] | Contingent Consideration [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of liabilities	$ 2,774,000	$ 2,733,000
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of liabilities	0	0
Level 1 [Member] | NLEX [Member] | Contingent Consideration [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of liabilities	0	0
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of liabilities	0	0
Level 2 [Member] | NLEX [Member] | Contingent Consideration [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of liabilities	0	0
Level 3 [Member] | NLEX [Member] | Contingent Consideration [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of liabilities	$ 2,774,000	$ 2,733,000