Pension and Other Post-retirement Benefits Components of Net Periodic Pension Expense (Details) (Pension Plans, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 4,760	$ 5,248
Expected return on plan assets	(5,518)	(6,050)
Amortization of actuarial loss	2,830	1,907
Total	$ 2,072	$ 1,105