Goodwill Changes in the Carrying Value of Goodwill (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Goodwill Roll Forward
Net carrying value at beginning of period	$ 119,509	$ 106,100	$ 106,100	$ 106,100
Acquisitions	10,197	0	23,606	0
Net carrying value at end of period	$ 129,706	$ 106,100	$ 129,706	$ 106,100