Summary of Significant Accounting Policies (Details 3) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended			9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Nonrecurring	Mar. 31, 2012 Nonrecurring	Sep. 30, 2011 Nonrecurring	Sep. 30, 2012 Nonrecurring	Sep. 30, 2011 Nonrecurring	Sep. 30, 2012 Nonrecurring Total	Sep. 30, 2011 Nonrecurring Total	Sep. 30, 2012 Nonrecurring Level 2	Sep. 30, 2011 Nonrecurring Level 2	Sep. 30, 2012 Nonrecurring Level 3	Sep. 30, 2011 Nonrecurring Level 3
Assets at fair value and gains (losses) recorded
Equipment held for sale	$ 8,117,000		$ 8,117,000		$ 20,648,000						$ 8,117,000	$ 4,501,000	$ 7,580,000	$ 4,169,000	$ 537,000	$ 332,000
Assets at fair value											8,117,000	4,501,000	7,580,000	4,169,000	537,000	332,000
Total losses on equipment held for sale						2,474,000		2,306,000	2,756,000	2,306,000
Total losses on assets						2,474,000		2,306,000	2,756,000	2,306,000
Asset write-down recorded earlier							300,000		300,000
Asset write-down	$ 2,474,000	$ 2,306,000	$ 2,756,000	$ 2,306,000		$ 2,500,000		$ 2,300,000		$ 2,300,000