Summary of Accrual Activities by Components Related to Company's Restructuring Charges (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost And Reserve [Line Items]
Accrued expense beginning balance		$ 1,736	$ 1,882
Restructuring charges		346	4,929	[1]
Reserves reversed			(322)
Cash payments		(1,212)	(4,181)
Non-cash write-offs and other adjustments		(64)	(572)
Accrued expense ending balance		806	1,736
Severance
Restructuring Cost And Reserve [Line Items]
Accrued expense beginning balance		611	1,358
Restructuring charges		185	2,738	[1]
Reserves reversed			(322)
Cash payments		(692)	(3,170)
Non-cash write-offs and other adjustments		(65)	7
Accrued expense ending balance		39	611
Facility
Restructuring Cost And Reserve [Line Items]
Accrued expense beginning balance		1,111	406
Restructuring charges		146	777	[1]
Cash payments		(503)	(104)
Non-cash write-offs and other adjustments		9	32
Accrued expense ending balance		763	1,111
Depreciation
Restructuring Cost And Reserve [Line Items]
Restructuring charges	[1]		616
Non-cash write-offs and other adjustments			(616)
Other Restructuring Charges
Restructuring Cost And Reserve [Line Items]
Accrued expense beginning balance	[2]	14	118
Restructuring charges	[2]	15	798	[1]
Cash payments	[2]	(17)	(907)
Non-cash write-offs and other adjustments	[2]	(8)	5
Accrued expense ending balance	[2]	$ 4	$ 14

[1] Excludes $1.6 million of gain on the sale of the Chatsworth, California facility.

[2] Other restructuring charges mainly related to consulting fees and relocation costs.