Non-Recourse Obligations of Variable Interest Entity (Schedule of Non-recourse Obligations) (Details) (USD $)	3 Months Ended		6 Months Ended										3 Months Ended		6 Months Ended							1 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 Letter of Credit	Jun. 30, 2012 Notes Payable to VIE Members	Dec. 31, 2011 Notes Payable to VIE Members	Jun. 30, 2012 Construction and Term Loan Facility	Dec. 31, 2011 Construction and Term Loan Facility	Jun. 30, 2012 Corporate Debt Securities	Dec. 31, 2011 Corporate Debt Securities	Jun. 30, 2012 LVE	Jun. 30, 2011 LVE	Jun. 30, 2012 LVE	Jun. 30, 2011 LVE	Dec. 31, 2011 LVE	Jun. 30, 2012 LVE Construction and Term Loan Facility	Dec. 31, 2011 LVE Construction and Term Loan Facility	Dec. 31, 2007 LVE Construction and Term Loan Facility	Jun. 30, 2012 LVE Construction Loans	Jul. 31, 2011 LVE Corporate Debt Securities	Dec. 31, 2007 LVE Corporate Debt Securities
Debt Instrument [Line Items]
Non-recourse obligations of variable interest entity, current	$ 31,621,000		$ 31,621,000		$ 29,686,000		$ 31,621,000	$ 29,686,000
Non-recourse debt of variable interest entity, long-term	192,479,000		192,479,000		192,980,000				119,479,000	119,980,000	73,000,000	73,000,000
Non-recourse obligations	224,100,000		224,100,000		222,666,000
Assets pledged as security not separately reported													163,800,000		163,800,000		163,805,507
Restricted investments held by variable interest entity	21,367,000		21,367,000		21,367,000								21,367,000		21,367,000		21,367,423
Net loss attributable to noncontrolling interest	1,668,000	2,692,000	1,045,000	5,482,000									100,000	2,600,000	600,000	(1,000,000)
Net cash provided by operating activities			108,773,000	97,568,000											(1,400,000)	(6,100,000)
Construction and term loan facility, maximum borrowing capacity																				143,500,000
Construction and term loan facility, amount outstanding																		119,500,000	120,000,000
Construction and term loan facility, repayments of principal, due in prior year																					4,200,000
Construction and term loan facility, loan maturities for remainder of current year																					83,100,000
Face amount																							100,000,000
Debt instrument, repayments made																						27,000,000
Letter of credit provided by VIE members as collateral on VIE debt						$ 10,000,000