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
Components of net periodic cost (benefit):
Service cost	$ 1,843	$ 1,586	$ 3,686		$ 3,171
Interest cost	6,654	6,565	13,308		13,130
Expected return on plan assets	(7,087)	(7,319)	(14,174)		(14,638)
Amortization of unrecognized prior service costs (benefits)	(181)	(181)	(362)	[1]	(361)
Amortization of losses (gains) from earlier periods	3,115	607	6,229	[1]	1,214
Net periodic cost (benefit)	4,344	1,258	8,687		2,516
Defined Benefit Pension Plan
Components of net periodic cost (benefit):
Service cost	1,509	1,175	3,017		2,349
Interest cost	5,997	5,739	11,994		11,477
Expected return on plan assets	(7,087)	(7,319)	(14,174)		(14,638)
Amortization of unrecognized prior service costs (benefits)	3	13	7		26
Amortization of losses (gains) from earlier periods	3,106	644	6,212		1,289
Net periodic cost (benefit)	3,528	252	7,056		503
Expected Employer contribution for the year			0
Payments to plan	0	2,690	0		4,714
Post-Retirement Medical Plan
Components of net periodic cost (benefit):
Service cost	264	206	528		412
Interest cost	126	130	253		260
Expected return on plan assets	0	0	0		0
Amortization of unrecognized prior service costs (benefits)	(417)	(427)	(835)		(853)
Amortization of losses (gains) from earlier periods	(157)	(130)	(315)		(260)
Net periodic cost (benefit)	(184)	(221)	(369)		(441)
Expected Employer contribution for the year			1,048
Payments to plan	391	84	524		215
Supplemental Executive Retirement Plan
Components of net periodic cost (benefit):
Service cost	70	205	141		410
Interest cost	531	696	1,061		1,393
Expected return on plan assets	0	0	0		0
Amortization of unrecognized prior service costs (benefits)	233	233	466		466
Amortization of losses (gains) from earlier periods	166	93	332		185
Net periodic cost (benefit)	1,000	1,227	2,000		2,454
Expected Employer contribution for the year			4,825
Payments to plan	$ 830	$ 882	$ 3,165		$ 1,789

[1] These accumulated other comprehensive income components are included in the computation of net periodic (benefit) cost of employee benefit plans (see Note 10 for additional details).