Acquisitions Cash Paid for Acquisitions (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash Paid for Business Acquisitions [Line Items]
Payments to Acquire Businesses, Gross	$ 74,465	$ 75,500	$ 65,102
Cash Paid for Holdback Payments made during the current year	12,307	1,460	0
Earnout and other payments related to Business Acquisitions	1,205	712	1,447
Payments to Acquire Businesses, Net of Cash Acquired	$ 87,977	$ 77,672	$ 66,549