Business Segment Information Business Segment Information (Schedule of Revenues And Assets Based On Location) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues	$ 261,635	$ 251,752	$ 241,237	$ 237,898	$ 226,247	$ 233,227	$ 237,760	$ 232,493	$ 992,522	$ 929,727	$ 900,835
Assets	1,309,824				1,294,559				1,309,824	1,294,559
United States [Member]
Revenues									843,407	785,506	767,068
Assets	1,066,451				1,098,643				1,066,451	1,098,643
International Operations [Member]
Revenues									149,115	144,221	133,767
Assets	$ 243,373				$ 195,916				$ 243,373	$ 195,916