Accounts Receivable and Inventory by Reportable Segments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts Receivable
Total accounts receivable	$ 83,955	$ 81,482
Inventories
Total inventories	104,764	91,278
Total segment assets	188,719	172,760
Photonics
Accounts Receivable
Total accounts receivable	31,536	33,490
Inventories
Total inventories	41,623	44,451
Vision
Accounts Receivable
Total accounts receivable	34,414	36,089
Inventories
Total inventories	42,498	33,836
Precision Motion
Accounts Receivable
Total accounts receivable	18,005	11,903
Inventories
Total inventories	$ 20,643	$ 12,991