SEGMENT INFORMATION (Operating information by segment) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 30, 2017	Sep. 28, 2019	Sep. 29, 2018	Sep. 30, 2017
Net revenue:
Net revenue		$ 139,827	$ 127,109	$ 115,908	$ 157,208	$ 184,824	$ 268,834	$ 221,772	$ 213,691	$ 540,052	$ 889,121	$ 809,041
Cost of sales :
Cost of sales										285,462	479,680	426,947
Gross profit :
Gross profit		65,438	58,780	55,573	74,799	85,823	126,969	99,447	97,202	254,590	409,441	382,094
Operating expenses:
Operating expenses										232,980	242,809	269,011
Income from operations:
Income from operations		$ 7,693	$ 1,827	$ (2,465)	$ 14,555	$ 24,574	$ 64,463	$ 38,436	$ 39,159	21,610	166,632	113,083
Capital Equipment
Net revenue:
Net revenue										386,820	719,390	651,934
Income from operations:
Income from operations	[1]									(12,577)	132,563	107,115
APS [Member]
Net revenue:
Net revenue										153,232	169,731	157,107
Income from operations:
Income from operations	[2]									$ 34,187	$ 34,069	$ 5,968

[1]     Fiscal (in thousands)   2019   2018   2017 Net revenue:                   Capital Equipment   $ 386,820
  $ 719,390
  $ 651,934
      APS   153,232
  169,731
  157,107
              Net revenue   540,052
  889,121
  809,041
Income from operations:                   Capital Equipment   (12,577 )   132,563
  107,115
      APS   34,187
  34,069
  5,968
              Income from operations   $ 21,610
  $ 166,632
  $ 113,083

[2]     Fiscal (in thousands)   2019   2018   2017 Net revenue:                   Capital Equipment   $ 386,820
  $ 719,390
  $ 651,934
      APS   153,232
  169,731
  157,107
              Net revenue   540,052
  889,121
  809,041
Income from operations:                   Capital Equipment   (12,577 )   132,563
  107,115
      APS   34,187
  34,069
  5,968
              Income from operations   $ 21,610
  $ 166,632
  $ 113,083