Geographic Information And Major Customers (Revenue From International Customers By Geographic Area) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	$ 115,294	$ 95,503	$ 103,518	$ 102,360	$ 89,253	$ 90,016	$ 82,246	$ 75,084	$ 416,675	$ 336,599	$ 264,013
Geographic revenue percentage	100.00%				100.00%				100.00%	100.00%	100.00%
U.S. [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue									216,365	200,183	174,976
Geographic revenue percentage	52.00%				59.00%				52.00%	59.00%	66.00%
United Kingdom [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue									94,338	59,571	46,416
Geographic revenue percentage	23.00%				18.00%				23.00%	18.00%	18.00%
Europe, Other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue									64,197	42,530	27,127
Geographic revenue percentage	15.00%				13.00%				15.00%	13.00%	10.00%
Other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue									$ 41,775	$ 34,315	$ 15,494
Geographic revenue percentage	10.00%				10.00%				10.00%	10.00%	6.00%