Business Combinations Business Combinations Pro Forma Information (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Business Acquisition [Line Items]
Revenues	$ 584,561,000	$ 616,446,000	$ 1,161,834,000	$ 1,184,176,000
Net income	28,352,000	32,063,000	50,571,000	56,478,000
Elimination of Acquisition Related Expenses [Member]
Business Acquisition [Line Items]
Significant non-recurring pro forma adjustments, net of estiamted tax	$ 3,800,000		$ 5,100,000