Segment And Geographic Information (Total Revenue By Geography) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Segment Reporting Information [Line Items]
Total revenue	$ 89,462	$ 83,297	$ 72,624	$ 63,296	$ 77,980	$ 76,336	$ 69,413	$ 66,811	$ 308,679	$ 290,540	$ 260,342
United States [Member]
Segment Reporting Information [Line Items]
Total revenue									230,359	211,711	189,517
Europe [Member]
Segment Reporting Information [Line Items]
Total revenue									32,998	37,921	35,072
Asia [Member]
Segment Reporting Information [Line Items]
Total revenue									17,637	16,260	13,694
Rest Of The World [Member]
Segment Reporting Information [Line Items]
Total revenue									$ 27,685	$ 24,648	$ 22,059