Retirement Plans Components of Net Periodic Benefit Cost (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Retirement Plans (Textuals) [Abstract]
Retirement eligible age for participation	55 years
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	$ 3,063	$ 2,975	$ 11,058
Interest cost	1,642	1,790	7,132
Expected return on plan assets	(5,350)	(4,855)	(19,922)
Amortization of prior service cost	13	15	58
Amortization of actuarial gain (loss)	532	325	1,384
Total net periodic benefit cost	(100)	250	(290)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Net period benefit cost for the pension and postretirement plans
Interest cost	35	39	150
Amortization of actuarial gain (loss)	0	(9)	(35)
Total net periodic benefit cost	$ 35	$ 30	$ 115