Inventories (Details) - USD ($) $ in Thousands	Jun. 28, 2015	Dec. 31, 2014
Inventory Disclosure [Abstract]
Raw materials and assembled parts	$ 58,540	$ 61,644
Service inventories, estimated current requirements	11,947	12,398
Work-in-process	86,275	76,402
Finished goods	24,897	25,996
Total current inventories	181,659	176,440
Non-current inventories	$ 48,703	$ 50,731