Employee Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Defined benefit pension plan
Components of net periodic cost (benefit):
Service cost	$ 1,627	$ 1,088	$ 4,146	$ 3,263
Interest cost	5,328	5,236	15,673	15,708
Expected return on plan assets	(6,317)	(5,459)	(18,375)	(16,348)
Amortization of unrecognized prior service cost (benefit)	13	12	38	38
Amortization of loss (gain) from earlier periods	4,212	3,086	12,001	7,456
Net periodic cost (benefit)	4,863	3,963	13,483	10,117
Expected Employer contribution for the year ended December 31, 2013			18,675
Payments to plan	14,624	4,300	16,649	17,600
Post-retirement medical plan
Components of net periodic cost (benefit):
Service cost	246	205	710	613
Interest cost	138	143	384	427
Amortization of unrecognized prior service cost (benefit)	(413)	(413)	(1,237)	(1,238)
Amortization of loss (gain) from earlier periods	(55)	(114)	(262)	(341)
Net periodic cost (benefit)	(84)	(179)	(405)	(539)
Expected Employer contribution for the year ended December 31, 2013			521
Payments to plan	109	109	391	348
Supplemental executive retirement plan
Components of net periodic cost (benefit):
Service cost	251	251	752	743
Interest cost	637	736	1,911	2,184
Amortization of unrecognized prior service cost (benefit)	233	235	699	700
Amortization of loss (gain) from earlier periods	325	184	975	478
Net periodic cost (benefit)	1,446	1,406	4,337	4,105
Expected Employer contribution for the year ended December 31, 2013			3,700
Payments to plan	$ 915	$ 698	$ 2,775	$ 2,094