Acquisitions (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended				12 Months Ended												12 Months Ended								3 Months Ended	12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Nov. 21, 2011	Dec. 31, 2011 National RP Support, Inc [Member]	Dec. 31, 2011 Quickparts, Inc. [Member]	Dec. 31, 2010 Quickparts, Inc. [Member]	Dec. 31, 2011 Accelerated Technologies, Inc [Member]	Dec. 31, 2011 Print3D Corporation [Member] months	Dec. 31, 2011 Sycode [Member]	Dec. 31, 2011 The3dStudio.com, Inc. [Member]	Dec. 31, 2011 Freedom Of Creation [Member]	Dec. 31, 2011 Alibre Inc [Member]	Dec. 31, 2011 Botmill Printer [Member] years	Dec. 31, 2011 Formero Pty, Ltd [Member] years	Sep. 30, 2011 Formero Pty, Ltd [Member]	Dec. 31, 2011 Kemo Modelmakerij B.V. [Member]	Dec. 31, 2011 RenShape [Member]	Dec. 31, 2011 Z Corporation And Vidar Systems [Member]	Dec. 31, 2010 Moeller Design And Development, Inc [Member]	Dec. 31, 2010 Design Prototyping Technologies, Inc [Member]	Dec. 31, 2010 CEP S.A. And Protometal S.A [Member]	Dec. 31, 2010 Express Pattern, Inc [Member]	Dec. 31, 2010 Bits From Bytes Limited [Member] years	Dec. 31, 2010 Provel, S.r.l. [Member]	Dec. 31, 2010 Provel, S.r.l. [Member] months	Dec. 31, 2009 Provel, S.r.l. [Member]
Business Acquisition [Line Items]
Date of acquisition													January 5, 2011	February 22, 2011		March 8, 2011	April 13, 2011	April 14, 2011	May 6, 2011	May 12, 2011	July 19, 2011	August 9, 2011	September 20, 2011		October 4, 2011	November 1, 2011	January 3, 2012	February 16, 2010	April 6, 2010	July 7, 2010	September 16, 2010	October 5, 2010		October 12, 2010
Fair value of the consideration paid													$ 5,550	$ 22,775		$ 1,000	$ 1,250	$ 500	$ 2,500	$ 2,286	$ 3,800	$ 17	$ 5,967		$ 3,719	$ 41,286	$ 135,488	$ 3,600	$ 3,600	$ 3,502	$ 1,650	$ 2,185	$ 11,955	$ 11,955
Bargain purchase gain																												37
Cash paid for business acquisition												137,000					1,000		1,875	1,136			4,967					2,600	3,000	2,426	1,400	1,592	6,848	6,848
Equity interest issued for business acquisition																	250		625	1,150			1,000					1,000	600	1,076	250	593	1,387	1,387
Lease term																												The lease provides for an initial term of five years with renewal options for two successive five-year terms	The lease provides for an initial term of approximately two years with renewal options for two-year and one-year successive terms, respectively	The leases current terms extend until June 30, 2012 and December 14, 2014, respectively, at which points the Company has certain renewal options.
Maximum earnout payment																	8,925					1,000	2,012										1,392	1,392
Future installment due in business acquisition																																1,420	3,720	3,720
Business acquisition agreement, period																	36					3	3									3		12
Accrued liability recorded for earnouts	1,862				3,297				1,862	3,297														1,862
Revenue	69,861	57,538	55,128	47,896	51,595	41,503	35,144	31,627	230,423	159,868	112,835			24,127																			1,117
Operating income	10,699	8,791	8,001	7,411	9,689	5,160	3,414	2,658	34,902	20,920	3,073			2,799																			257
Pro forma revenue														233,612	185,055																			163,965	119,005
Pro forma net income														$ 34,144	$ 20,102																			$ 20,056	$ 1,214