Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Carrying Amount	$ 209,597	$ 249,120
Fair Value	218,550	255,440
Fixed rate long-term notes payable [Member]
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Carrying Amount	179,160	196,242
Fair Value	186,918	199,292
Long-term notes payable, non-recourse [Member]
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Carrying Amount	954	15,991
Fair Value	966	16,157
Debenture bonds [Member]
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Carrying Amount	29,483	36,887
Fair Value	$ 30,666	$ 39,991