Acquisitions Of Businesses (Details) (USD $)	0 Months Ended	6 Months Ended	12 Months Ended
	Jan. 04, 2012 Company	Jun. 30, 2011 Company	Dec. 31, 2012	Dec. 31, 2011 Company	Dec. 31, 2010 Company
Business Acquisition [Line Items]
Business acquisition date			Jan. 04, 2012
Number of businesses acquired	1	1		2	2
Non-cash income from contingent consideration arrangements			$ 6,381,000	$ 2,798,000	$ 394,000
USM
Business Acquisition [Line Items]
Business acquisition date		Jun. 30, 2011
Business acquisition, percentage of voting interests acquired		100.00%
Purchase price		251,000,000
Working capital acquired		5,000,000
Other net liabilities acquired		21,300,000
Ascribed goodwill		130,300,000
Ascribed identifiable intangible assets		137,000,000