Segment Information (Revenue by Georgraphic Location) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenue by geographic location
Revenue	$ 100,848	$ 98,388	$ 93,586	$ 78,243	$ 76,702	$ 78,628	$ 78,303	$ 79,195	$ 371,065	$ 312,828	$ 258,785
U.S. [Member]
Revenue by geographic location
Revenue									319,649	272,945	222,304
Other countries [Member]
Revenue by geographic location
Revenue									$ 51,416	$ 39,883	$ 36,481