Retirement Plans Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Age of Eligibility of Plan			55 years
Retirement Plans (Textuals) [Abstract]
Years of service required for eligibility in plan			5 years
Pension Plans, Defined Benefit [Member]
Net period benefit cost for the pension and postretirement plans
Service cost	$ 3,062	$ 2,975	$ 6,125	$ 5,950	$ 11,058
Interest cost	1,643	1,790	3,285	3,580	7,132
Expected return on plan assets	(5,350)	(4,855)	(10,700)	(9,710)	(19,922)
Amortization of prior service cost	12	15	25	30	58
Amortization of actuarial gain (loss)	533	325	1,065	650	1,384
Total net periodic benefit cost	(100)	250	(200)	500	(290)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Net period benefit cost for the pension and postretirement plans
Interest cost	35	39	70	78	150
Amortization of actuarial gain (loss)	0	(9)	0	(18)	(35)
Total net periodic benefit cost	$ 35	$ 30	$ 70	$ 60	$ 115