Note 6. Employee Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Qualified Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligation	$ 18,181	$ 18,871
Expected return on plan assets	(21,740)	(23,327)
Amortization of actuarial loss (gain)	3,123	2,475
Amortization of prior-service costs (credits)	405	404
Settlement loss	60	0
Net periodic benefit expense (income)	29	(1,577)
Non Qualified Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligation	796	862
Amortization of actuarial loss (gain)	296	219
Amortization of prior-service costs (credits)	1	1
Net periodic benefit expense (income)	1,093	1,082
Postretirement Medical Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	293	271
Interest cost on benefit obligation	645	672
Amortization of actuarial loss (gain)	(65)	(657)
Amortization of prior-service costs (credits)	(614)	(716)
Net periodic benefit expense (income)	$ 259	$ (430)