Fair Value Measurements (Details 3) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Carrying Amount
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Fair value of long-term debt	$ 280,486	$ 293,068
Fair Value
Fair value of long-term debt estimated using quoted market prices or discounted future cash flows
Fair value of long-term debt	284,188	299,851
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	241,111	250,970
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	244,101	256,756
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	39,375	42,098
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	$ 40,087	$ 43,095