Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 28, 2013		Jun. 29, 2012		Jun. 28, 2013		Jun. 29, 2012
Numerators:
Consolidated net income	$ 842		$ 4,467		$ 2,311		$ 5,544
Less: Income attributable to noncontrolling interest	(18)		(8)		(54)		(26)
Income from continuing operations	824		4,459		2,257		5,518
Income (loss) from discontinued operations	(1,695)		414		(1,046)		736
Net income (loss) attributable to GSI Group Inc.	$ (871)		$ 4,873		$ 1,211		$ 6,254
Denominators:
Weighted average common shares outstanding- basic	34,088		33,782		34,036		33,731
Dilutive potential common shares	197	[1]	171	[1]	243	[1]	184	[1]
Weighted average common shares outstanding - diluted	34,285		33,953		34,279		33,915
Antidilutive common shares excluded from above	570				472
Basic Earnings (Loss) per Common Share:
From continuing operations	$ 0.02		$ 0.13		$ 0.07		$ 0.16
From discontinued operations	$ (0.05)		$ 0.01		$ (0.03)		$ 0.03
Basic earnings (loss) per share attributable to GSI Group Inc.	$ (0.03)		$ 0.14		$ 0.04		$ 0.19
Diluted Earnings (Loss) per Common Share:
From continuing operations	$ 0.02		$ 0.13		$ 0.07		$ 0.16
From discontinued operations	$ (0.05)		$ 0.01		$ (0.03)		$ 0.02
Diluted earnings (loss) per share attributable to GSI Group Inc.	$ (0.03)		$ 0.14		$ 0.04		$ 0.18

[1] Due to the Company's net loss attributable to GSI Group Inc. for the three months ended June 28, 2013, all potentially dilutive shares were excluded as their effect would have been anti-dilutive.