Employee Benefit Plans (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Components of net periodic cost
Service cost	$ 6,158	$ 5,473
Interest cost	24,426	24,007
Defined benefit pension plan
Expected benefit payments for the Defined Benefit Pension, Post-Retirement Medical and Supplemental Executive Retirement plans
2013	13,621
2014	14,259
2015	15,136
2016	16,640
2017	17,708
2018 through 2022	112,582
Components of net periodic cost
Service cost	4,350	3,935	3,739
Interest cost	20,945	20,286	19,578
Expected return on plan assets	(21,797)	(21,093)	(18,618)
Amortization of transition obligation		(1,388)	(1,514)
Amortization of unrecognized prior service cost (benefit)	51	51	82
Amortization of loss (gain) from earlier periods	9,941	5,115	5,091
Net periodic (benefit) cost	13,490	6,906	8,358
Post-retirement medical plan
Expected benefit payments for the Defined Benefit Pension, Post-Retirement Medical and Supplemental Executive Retirement plans
2013	637
2014	697
2015	727
2016	743
2017	771
2018 through 2022	4,166
Components of net periodic cost
Service cost	817	622	728
Interest cost	569	585	713
Amortization of unrecognized prior service cost (benefit)	(1,650)	(1,650)	(1,650)
Amortization of loss (gain) from earlier periods	(455)	(611)	(461)
Net periodic (benefit) cost	(719)	(1,054)	(670)
Supplemental executive retirement plan
Expected benefit payments for the Defined Benefit Pension, Post-Retirement Medical and Supplemental Executive Retirement plans
2013	3,720
2014	3,529
2015	4,940
2016	3,390
2017	18,909
2018 through 2022	13,813
Components of net periodic cost
Service cost	991	916	673
Interest cost	2,912	3,136	2,905
Amortization of unrecognized prior service cost (benefit)	934	2,584	899
Amortization of loss (gain) from earlier periods	637	145
Net periodic (benefit) cost	$ 5,474	$ 6,781	$ 4,477