Fair Value Measurements - Schedule of Assets and Liabilities Carried at Fair Value Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Municipal notes and bonds	$ 70,005	$ 109,589
Foreign currency forward exchange contracts	156	45
Total assets	70,161	109,634
Contingent consideration - acquisitions	2,139	2,593
Total liabilities	2,139	2,593
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Municipal notes and bonds	0	0
Foreign currency forward exchange contracts	0	0
Total assets	0	0
Contingent consideration - acquisitions	0	0
Total liabilities	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Municipal notes and bonds	70,005	109,589
Foreign currency forward exchange contracts	156	45
Total assets	70,161	109,634
Contingent consideration - acquisitions	0	0
Total liabilities	0	0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Municipal notes and bonds	0	0
Foreign currency forward exchange contracts	0	0
Total assets	0	0
Contingent consideration - acquisitions	2,139	2,593
Total liabilities	$ 2,139	$ 2,593