RESTRUCTURING COSTS (Details) $ in Thousands		3 Months Ended		9 Months Ended
		Jul. 31, 2017 USD ($)	Jul. 31, 2016 USD ($)	Jul. 31, 2017 USD ($) employee	Jul. 31, 2016 USD ($)
Activity and balance of the restructuring liability accounts
Balance at beginning of period				$ 2,838	$ 1,279
Additional liability recorded		$ 2,203	$ 1,138	8,874	2,057
Additional liability recorded					2,058
Cash payments				(6,049)	(2,052)
Balance at end of period		5,663	1,285	5,663	1,285
Current restructuring liabilities		5,663	1,285	5,663	1,285
Non-current restructuring liabilities		0	0	$ 0	0
Workforce reduction
Restructuring Cost and Reserve [Line Items]
Number of employee reduction | employee	[1]			60
Activity and balance of the restructuring liability accounts
Balance at beginning of period				$ 868	591
Additional liability recorded	[1]			3,967
Additional liability recorded					2,067
Cash payments				(3,370)	(1,736)
Balance at end of period		1,465	922	1,465	922
Current restructuring liabilities		1,465	922	1,465	922
Non-current restructuring liabilities		0	0	0	0
Consolidation of excess facilities
Activity and balance of the restructuring liability accounts
Balance at beginning of period				1,970	688
Additional liability recorded	[2]			4,907
Additional liability recorded					(9)
Cash payments				(2,679)	(316)
Balance at end of period		4,198	363	4,198	363
Current restructuring liabilities		4,198	363	4,198	363
Non-current restructuring liabilities		$ 0	$ 0	$ 0	$ 0

[1] Reflects a global workforce reduction of approximately 60 employees during fiscal 2017 as part of a business optimization strategy to improve gross margin, constrain operating expense and redesign certain business processes and systems.

[2] Reflects unfavorable lease commitments and relocation costs incurred during fiscal 2017 in connection with the facility transition from Ciena's existing research and development center located at Lab 10 on the former Nortel Carling Campus to a new campus facility in Ottawa, Canada.