CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Statement Of Income And Comprehensive Income [Abstract]
Consolidated net income (loss)	$ (24,242)		$ 7,331		$ 19,578
Other comprehensive income (loss):
Foreign currency translation adjustments, net of tax	(6,968)	[1]	54	[1]	(1,510)	[1]
Pension liability adjustments, net of tax	(3,146)	[2]	3,353	[2]	(3,215)	[2]
Total other comprehensive income (loss)	(10,114)		3,407		(4,725)
Total consolidated comprehensive income (loss)	(34,356)		10,738		14,853
Less: Comprehensive income attributable to noncontrolling interest	(10)		(22)		(40)
Comprehensive income (loss) attributable to GSI Group Inc.	$ (34,366)		$ 10,716		$ 14,813

[1] The tax effect on this component of comprehensive income was $622, $477 and $1,942 in 2014, 2013 and 2012, respectively.

[2] The tax effect on this component of comprehensive income was ($906), $900 and ($829) in 2014, 2013 and 2012, respectively.