Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Components of net periodic cost (benefit):
Service cost	$ 1,845	$ 1,721	$ 5,530	$ 4,892
Interest cost	6,694	6,498	20,002	19,628
Expected return on plan assets	(7,084)	(7,328)	(21,258)	(21,966)
Amortization of unrecognized prior service costs (benefits)	(159)	(181)	(520)	(542)
Amortization of losses (gains) from earlier periods	3,268	973	9,497	2,187
Settlement	0	2,666	0	2,666
Net periodic cost (benefit)	4,564	4,349	13,251	6,865
Defined Benefit Pension Plan
Components of net periodic cost (benefit):
Service cost	1,521	1,364	4,538	3,713
Interest cost	5,996	5,824	17,990	17,301
Expected return on plan assets	(7,084)	(7,328)	(21,258)	(21,966)
Amortization of unrecognized prior service costs (benefits)	3	12	10	38
Amortization of losses (gains) from earlier periods	3,086	885	9,298	2,174
Settlement	0	0	0	0
Net periodic cost (benefit)	3,522	757	10,578	1,260
Expected Employer contribution for the year			0
Payments to plan	0	6,003	0	10,717
Post-Retirement Medical Plan
Components of net periodic cost (benefit):
Service cost	254	327	781	739
Interest cost	167	171	420	431
Expected return on plan assets	0	0	0	0
Amortization of unrecognized prior service costs (benefits)	(395)	(427)	(1,230)	(1,280)
Amortization of losses (gains) from earlier periods	16	(77)	(298)	(337)
Settlement	0	0	0	0
Net periodic cost (benefit)	42	(6)	(327)	(447)
Expected Employer contribution for the year			1,466
Payments to plan	576	178	1,100	393
Supplemental Executive Retirement Plan
Components of net periodic cost (benefit):
Service cost	70	30	211	440
Interest cost	531	503	1,592	1,896
Expected return on plan assets	0	0	0	0
Amortization of unrecognized prior service costs (benefits)	233	234	700	700
Amortization of losses (gains) from earlier periods	166	165	497	350
Settlement	0	2,666	0	2,666
Net periodic cost (benefit)	1,000	3,598	3,000	6,052
Expected Employer contribution for the year			4,825
Payments to plan	$ 830	$ 14,255	$ 3,995	$ 16,044