Note 6. Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Qualified Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligation	$ 18,211	$ 18,767	$ 36,392	$ 37,638
Expected return on plan assets	(21,727)	(23,309)	(43,467)	(46,636)
Amortization of actuarial loss (gain)	3,241	2,375	6,364	4,850
Amortization of prior-service costs (credits)	404	405	809	809
Settlement loss	(22)	0	38	0
Net periodic benefit expense (income)	107	(1,762)	136	(3,339)
Non Qualified Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligation	797	864	1,593	1,726
Amortization of actuarial loss (gain)	305	219	601	438
Amortization of prior-service costs (credits)	1	1	2	2
Net periodic benefit expense (income)	1,103	1,084	2,196	2,166
Postretirement Medical Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	171	271	464	542
Interest cost on benefit obligation	625	671	1,270	1,343
Amortization of actuarial loss (gain)	(176)	(656)	(241)	(1,313)
Amortization of prior-service costs (credits)	(613)	(716)	(1,227)	(1,432)
Net periodic benefit expense (income)	$ 7	$ (430)	$ 266	$ (860)