Reportable Operating Segments (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Revenues and total assets by geographic area
Revenues	$ 409,995	$ 291,573
% of revenue	100.00%	100.00%
Total Assets	908,535		931,207
United States
Revenues and total assets by geographic area
Revenues	405,163	289,128
% of revenue	98.80%	99.20%
Total Assets	896,330		920,872
Non-United States
Revenues and total assets by geographic area
Revenues	4,832	2,445
% of revenue	1.20%	0.80%
Total Assets	$ 12,205		$ 10,335