Business Segments (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenue	$ 125,200	$ 123,869	$ 134,918	$ 117,880	$ 117,220	$ 113,197	$ 104,899	$ 101,373	$ 501,867	$ 436,689	$ 401,572
United States
Segment Reporting Information [Line Items]
Revenue									380,052	347,251	323,867
United Kingdom
Segment Reporting Information [Line Items]
Revenue									83,652	65,578	61,102
Other Countries
Segment Reporting Information [Line Items]
Revenue									$ 38,163	$ 23,860	$ 16,603