Business Segments (Details 3) (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
Revenue	$ 105,985	$ 99,671	$ 102,311	$ 93,605	$ 93,892	$ 88,948	$ 86,034	$ 64,293	$ 401,572	$ 333,167	$ 259,926
United States [Member]
Revenue									323,867	274,010	214,194
United Kingdom [Member]
Revenue									61,102	48,151	36,518
Other Regions [Member]
Revenue									$ 16,603	$ 11,006	$ 9,214