Operations and Summary of Significant Accounting Policies (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Balance at the beginning of the year
Goodwill	$ 121,053	$ 89,991
Accumulated impairment losses	(21,204)	(19,922)
Goodwill at the beginning of the period, net	99,849	70,069
Goodwill acquired	22,826	32,230
Foreign exchange	496	(833)
Impairment	(2,346)	(1,282)	(6,292)
Reclassifications	1,156	(335)
Balance at the end of the year
Goodwill	145,531	121,053	89,991
Accumulated impairment losses	(23,550)	(21,204)	(19,922)
Goodwill at the end of the period, net	121,981	99,849	70,069
North America
Balance at the beginning of the year
Goodwill	84,567	52,427
Accumulated impairment losses	(10,666)	(10,666)
Goodwill at the beginning of the period, net	73,901	41,761
Goodwill acquired	3,581	32,230
Foreign exchange	101	(90)
Reclassifications	1,156
Balance at the end of the year
Goodwill	89,405	84,567
Accumulated impairment losses	(10,666)	(10,666)
Goodwill at the end of the period, net	78,739	73,901
Europe
Balance at the beginning of the year
Goodwill	34,538	35,623
Accumulated impairment losses	(10,538)	(9,256)
Goodwill at the beginning of the period, net	24,000	26,367
Goodwill acquired	19,245
Foreign exchange	364	(750)
Impairment	(2,346)	(1,282)	(6,292)
Reclassifications		(335)
Balance at the end of the year
Goodwill	54,147	34,538	35,623
Accumulated impairment losses	(12,884)	(10,538)	(9,256)
Goodwill at the end of the period, net	41,263	24,000	26,367
Asia/Pacific
Balance at the beginning of the year
Goodwill	1,948	1,941
Goodwill at the beginning of the period, net	1,948	1,941
Foreign exchange	31	7
Balance at the end of the year
Goodwill	1,979	1,948
Goodwill at the end of the period, net	1,979	1,948
Australia
Carrying amount of goodwill by reportable segment
Marginal percentage by which the company passed annual impairment test	8.00%
Balance at the end of the year
Goodwill	2,000
Number of locations into which the activities will be consolidated	3
United States
Balance at the end of the year
Number of locations into which the activities will be consolidated	4
S&P Clever
Carrying amount of goodwill by reportable segment
Marginal percentage by which the company passed annual impairment test	2.00%
Balance at the end of the year
Goodwill	$ 19,900
Number of locations into which the activities will be consolidated	7