Fair Value Measurements (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Carrying Amount
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Fair value of long-term debt	$ 311,243	$ 299,941
Fair Value
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Fair value of long-term debt	314,191	317,440
Level 2 | Notes payable | Carrying Amount
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Fair value of long-term debt	270,112	263,745
Level 2 | Notes payable | Fair Value
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Fair value of long-term debt	271,716	279,505
Level 2 | Nonrecourse | Notes payable | Carrying Amount
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Fair value of long-term debt		785
Level 2 | Nonrecourse | Notes payable | Fair Value
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Fair value of long-term debt		800
Level 1 | Debenture bonds | Carrying Amount
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Fair value of long-term debt	41,131	35,411
Level 1 | Debenture bonds | Fair Value
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Fair value of long-term debt	$ 42,475	$ 37,135