Segment and Geographic Information (Details) (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 segment	Dec. 31, 2013	Dec. 31, 2012
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	$ 90,567	$ 86,445	$ 44,857	$ 94,163	$ 116,926	$ 36,901	$ 126,165	$ 57,672	$ 316,032	$ 337,664	$ 219,058
Long-Lived Assets	469,581				1,364,611				469,581	1,364,611	1,316,111
Number of reportable segments									1
United States [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									6,729	8,368	11,877
Long-Lived Assets	35,540				113,888				35,540	113,888	123,977
United Kingdom [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									309,303	329,296	207,181
Long-Lived Assets	434,042				1,247,248				434,042	1,247,248	1,189,870
Other Countries [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Long-Lived Assets	(1)				3,475				(1)	3,475	2,264
Total International [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									309,303	329,296	207,181
Long-Lived Assets	$ 434,041				$ 1,250,723				$ 434,041	$ 1,250,723	$ 1,192,134