Reportable Operating Segments (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Revenues and total assets by geographic area
Revenue	$ 551,333	$ 431,842	$ 1,406,341	$ 1,060,851
% of Revenue	100.00%	100.00%	100.00%	100.00%
Total Assets	1,019,011		1,019,011		931,207
United States
Revenues and total assets by geographic area
Revenue			1,393,837	1,053,547
% of Revenue			99.10%	99.30%
Total Assets	1,007,980		1,007,980		920,872
Non-United States
Revenues and total assets by geographic area
Revenue			12,504	7,304
% of Revenue			0.90%	0.70%
Total Assets	$ 11,097		$ 11,097		$ 10,335