Fair Value Measurements - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Details) - Recurring [Member] - USD ($)	Jun. 30, 2018	Dec. 31, 2017
NLEX [Member] | Contingent Consideration [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of liabilities	$ 1,618,000	$ 2,774,000
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	$ 1,618,000	$ 2,774,000