Business Segments (Details 3) (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
Segment Reporting Information [Line Items]
Revenue	$ 117,220	$ 113,197	$ 104,899	$ 101,373	$ 105,985	$ 99,671	$ 102,311	$ 93,605	$ 436,689	$ 401,572	$ 333,167
United States [Member]
Segment Reporting Information [Line Items]
Revenue									347,251	323,867	274,010
United Kingdom [Member]
Segment Reporting Information [Line Items]
Revenue									65,578	61,102	48,151
Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue									$ 23,860	$ 16,603	$ 11,006