Employee Benefit Plans (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			1 Months Ended
	Dec. 31, 2014 plans	Dec. 31, 2013 plans	Dec. 31, 2012	Apr. 30, 2008
Defined Benefit Plan Disclosure [Line Items]
Number of defined benefit plans	4	4
Accumulated other comprehensive income (loss)	$ 29,899	$ 26,216	$ 37,828
Accumulated benefit obligations in excess of aggregate projected benefit obligation	41,214	39,955
Accumulated benefit obligations in excess of aggregate accumulated benefit obligation	41,214	39,955
Accumulated benefit obligations in excess of aggregate fair value of plan assets	0	0
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Defined Contribution Plan, Cost Recognized	1,219	1,190	1,161
Qualified Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of defined benefit plans	2
Non-qualified Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of defined benefit plans	1
Supplemental Employee Retirement Plans [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2015	0
2016	0
2017	0
2018	29,641
2019	10,383
2020 — 2024	2,100
Postretirement Medical [Member]
Defined Benefit Plan Disclosure [Line Items]
Number Of Participating Employees	244
Employee Contribution Percentage	100.00%
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2015	607
2016	597
2017	598
2018	596
2019	596
2020 — 2024	2,944
Life Insurance Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Number Of Participating Employees	172
Postretirement Life Insurance [Member]
Defined Benefit Plan Disclosure [Line Items]
Number Of Participating Employees	411
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of defined benefit plans	3
Accumulated other comprehensive income (loss)	30,481	27,102	37,646
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2015	10,232
2016	9,843
2017	9,505
2018	38,773
2019	19,093
2020 — 2024	40,058
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated other comprehensive income (loss)	(582)	(886)	182
Houly Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Period For Amortization of Benefit Plan Gains and Losses (in years)	16 years 0 months 7 days
Salaried Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Period For Amortization of Benefit Plan Gains and Losses (in years)	16 years 8 months 21 days
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of Excess in Projected Benefit Obligation and Fair Value Assets To Be Amortized	10.00%
Minimum [Member] | Supplemental Employee Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Age Requirement For Plant Participation	60
Required employment period	8 years
Ten Year Rate of Return [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual Rate of Return Period (in years)	10 years
Actual Rate of Return On Plan Assets	6.60%	7.20%	7.50%
Five Year Rate of Return [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual Rate of Return Period (in years)	5 years
Actual Rate of Return On Plan Assets	9.80%	13.60%	2.90%
President and Chief Executive Officer [Member] | Supplemental Employee Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Additional SERP Benefit				$ 736
Service Period Credit Upon Termination				36 months