Acquisitions (Purchase Price Allocation) (Details) (USD $)							12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Two Thousand Twelve [Member]	Dec. 31, 2013 Prime [Member]	Dec. 31, 2013 Two Thousand Thirteen [Member]	Dec. 31, 2011 Prime [Member]
Business Acquisition [Line Items]
Purchase price allocation, Accounts receivables				$ 15,175,000	$ 8,149,000	$ 22,666,000
Purchase price allocation, Other current assets				1,240,000	496,000	922,000
Purchase price allocation, Property and equipment				32,387,000	3,996,000	14,392,000
Goodwill	518,743,000	442,143,000	364,687,000	75,407,000	90,654,000	78,646,000
Purchase price allocation, Customer relationship intangible assets				5,932,000	9,400,000	19,727,000
Purchase price allocation, Other noncurrent assets				623,000	100,000	12,000
Purchase price allocation, Accounts payable and other liabilities				41,787,000	(16,033,000)	35,717,000
Purchase price allocation, Total				88,977,000	96,762,000	100,648,000
Measurement period adjustment, Deferred tax asset							590,000
Measurement period adjustment, Deferred tax liabilities							300,000
Measurement period adjustment, Goodwill							$ 300,000