CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 26, 2014		Sep. 27, 2013		Sep. 26, 2014		Sep. 27, 2013
Statement Of Income And Comprehensive Income [Abstract]
Consolidated net income	$ 4,525		$ 1,778		$ 6,243		$ 3,043
Other comprehensive income (loss):
Foreign currency translation adjustments, net of tax	(3,845)	[1]	3,764	[1]	(2,902)	[1]	(2,016)	[1]
Pension liability adjustments, net of tax	435	[2]	(370)	[2]	449	[2]	802	[2]
Total other comprehensive income (loss)	(3,410)		3,394		(2,453)		(1,214)
Total consolidated comprehensive income	1,115		5,172		3,790		1,829
Less: Comprehensive (income) loss attributable to noncontrolling interest			12		(10)		(42)
Comprehensive income attributable to GSI Group Inc.	$ 1,115		$ 5,184		$ 3,780		$ 1,787

[1] The tax effect on this component of comprehensive income was $0.4 million and $0.2 million for the three and nine months ended September 26, 2014, respectively. The impact was zero and $1.3 million for the three and nine months ended September 27, 2013, respectively.

[2] The tax effect on this component of comprehensive income was not material for all periods presented. See Note 4 for the total amount of pension liability adjustments reclassified out of accumulated other comprehensive income (loss).