Segment Information Segment Information (Schedule of Revenue by Geographic Area) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues	$ 143,299	$ 151,911	$ 117,540	$ 112,384	$ 109,927	$ 152,891	$ 112,370	$ 122,233	$ 525,134	$ 497,421	$ 539,447
United States
Revenues									516,466	490,409	532,862
Canada
Revenues									5,180	4,646	5,959
Mexico
Revenues									$ 3,488	$ 2,366	$ 626