Segment Information (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Segment Information [Line Items]
Total revenues	$ 302,486	$ 262,228
London Operation [Member]
Segment Information [Line Items]
Total revenues	$ 2,700	$ 2,400	$ 9,100