Employee Benefit Plans (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Components of Net Periodic Benefit Cost
Service cost	$ 4,473,000	$ 3,363,000	$ 11,676,000	$ 10,013,000
Interest cost	6,340,000	6,876,000	18,939,000	20,588,000
Expected return on plan assets	(4,065,000)	(4,022,000)	(12,196,000)	(12,048,000)
Recognized net actuarial loss	2,280,000	1,863,000	6,381,000	5,338,000
Net periodic benefit cost	9,028,000	8,080,000	24,800,000	23,891,000
Employer contribution	$ 11,900,000		$ 18,600,000