Employee Benefit Plans (Postretirement Medical Plan) (Details) (Postretirement Medical Plan [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Postretirement Medical Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the year		$ 1,441	$ 1,405	$ 1,539
Interest cost on benefit obligation		4,492	4,832	5,578
Net periodic benefit expense (income)		4,721	5,035	5,895
Actuarial loss (gain)		3,493	2,354	(10,353)
Plan amendments			(198)
Amortization of prior-service credit	1,200	(1,212)	(1,202)	(1,222)
Loss (gain) recognized in other comprehensive income or loss		$ 4,705	$ 3,358	$ (9,131)
Discount rate		5.00%	5.65%	6.38%