Segment Reporting (Details) (USD $)	3 Months Ended			9 Months Ended			9 Months Ended	3 Months Ended			6 Months Ended	9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2014 segment	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 Restructuring accruals recorded in 2012 and 2011	Sep. 30, 2014 U.S. Operations	Sep. 30, 2013 U.S. Operations	Jun. 30, 2013 U.S. Operations	Jun. 30, 2013 U.S. Operations	Sep. 30, 2014 U.S. Operations	Sep. 30, 2013 U.S. Operations	Sep. 30, 2014 Canadian Operations	Sep. 30, 2013 Canadian Operations	Sep. 30, 2014 Canadian Operations	Sep. 30, 2013 Canadian Operations	Sep. 30, 2014 European Operations	Sep. 30, 2013 European Operations	Sep. 30, 2014 European Operations	Sep. 30, 2013 European Operations	Sep. 30, 2014 Asia Pacific Operations	Sep. 30, 2013 Asia Pacific Operations	Sep. 30, 2014 Asia Pacific Operations	Sep. 30, 2013 Asia Pacific Operations
Segment Reporting
Number of operating segments				4
Segment reporting
Total revenues	$ 134,773,000	$ 127,558,000		$ 410,848,000	$ 398,901,000			$ 72,540,000	$ 76,843,000			$ 225,531,000	$ 242,687,000	$ 17,946,000	$ 17,575,000	$ 55,194,000	$ 56,224,000	$ 31,677,000	$ 22,663,000	$ 95,605,000	$ 65,407,000	$ 12,610,000	$ 10,477,000	$ 34,518,000	$ 34,583,000
Income (loss) before income tax expense (benefit)	12,078,000	10,690,000		47,186,000	32,412,000			1,049,000	4,478,000			10,542,000	14,779,000	3,203,000	2,749,000	11,306,000	9,120,000	7,518,000	4,115,000	26,968,000	10,436,000	308,000	(652,000)	(1,630,000)	(1,923,000)
Identifiable assets	4,024,994,000	3,157,310,000		4,024,994,000	3,157,310,000	2,209,887,000		978,246,000	1,377,616,000			978,246,000	1,377,616,000	110,224,000	137,389,000	110,224,000	137,389,000	2,262,568,000	1,128,133,000	2,262,568,000	1,128,133,000	673,956,000	514,172,000	673,956,000	514,172,000
Duplicate rent charges											2,600,000
One-time charge upon completion of the move										3,900,000
Facility closing expense			1,600,000
Reduction in previously recorded restructuring accruals							1,600,000
Restructuring charges					(75,000)
Carrying value of goodwill	$ 14,332,000			$ 14,332,000