Employee Benefit Plans (Schedule of Net Periodic Benefit Cost and Other Amounts Recognized) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other changes in plan assets and benefits obligations recognized in other comprehensive income
Total recognized in other comprehensive (income) loss	$ 3,860	$ (2,350)	$ (2,440)
Postretirement Medical Plan [Member]
Net periodic benefit cost
Service cost	24	32	146
Interest cost	118	126	399
Expected return on plan assets
Amortization of transition obligation (asset)
Amortization of prior service costs	(1,737)	(1,703)	(244)
Amortization of net (gain) or loss	(227)	(132)
Total net periodic benefit cost	(1,822)	(1,677)	301
Other changes in plan assets and benefits obligations recognized in other comprehensive income
Prior service cost for the period		(91)	(3,851)
Net (gain) or loss for the period	558	(668)	(1,355)
Amortization of transition obligation (asset)
Amortization of prior service costs	1,737	1,703	244
Amortization of net gain or (loss)	227	132
Total recognized in other comprehensive (income) loss	2,522	1,076	(4,962)
Total recognized in net periodic benefit cost and other comprehensive income	700	(601)	(4,661)
Weighted average assumptions used:
Discount rate	5.20%	4.30%	5.20%
Expected return on plan assets
Rate of compensation increases
Impact of one-percentage point change in assumed health care cost trend rates:
Effect on service cost and interest cost, Increase	10
Effect on service cost and interest cost, Decrease	(8)
Effect on postretirement obligation, Increase	254
Effect on postretirement obligation, Decrease	(198)
Postretirement Medical Plan [Member] | Pre-65 [Member]
Assumed health care cost trend rates:
Health care cost trend rate assumed for current year	7.75%	8.25%	8.25%
Ultimate rate	5.00%	5.00%	5.00%
Year that ultimate rate is reached	2022	2022	2021
Measurement date	December 31, 2014	December 31, 2013	December 31, 2012
Postretirement Medical Plan [Member] | Post-65 [Member]
Assumed health care cost trend rates:
Health care cost trend rate assumed for current year	25.00%	35.00%	57.00%
Ultimate rate	5.00%	5.00%	5.00%
Year that ultimate rate is reached	2022	2022	2019
Measurement date	December 31, 2014	December 31, 2013	December 31, 2012
Pension Plan [Member]
Net periodic benefit cost
Service cost
Interest cost	796	732	761
Expected return on plan assets	(1,257)	(948)	(817)
Amortization of transition obligation (asset)
Amortization of prior service costs	3
Amortization of net (gain) or loss		97	70
Total net periodic benefit cost	(458)	(119)	14
Other changes in plan assets and benefits obligations recognized in other comprehensive income
Prior service cost for the period		93
Net (gain) or loss for the period	3,117	(4,696)	1,000
Amortization of transition obligation (asset)
Amortization of prior service costs	(3)
Amortization of net gain or (loss)		(97)	(70)
Total recognized in other comprehensive (income) loss	3,114	(4,700)	930
Total recognized in net periodic benefit cost and other comprehensive income	2,656	(4,819)	944
Weighted average assumptions used:
Discount rate	5.10%	4.30%	5.10%
Expected return on plan assets	7.50%	7.50%	7.50%
Rate of compensation increases
Estimated amounts that will be amortized from accumulated other comprehensive income in the next fiscal year:
Transition obligation (asset)
Prior service cost	3	3
Net actuarial (gain) or loss	$ 31		$ 97