Retirement Plans Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Retirement Plans (Textuals) [Abstract]
Defined Benefit Plan, Age of Eligibility of Plan			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	$ 2,318	$ 2,975	$ 8,443	$ 8,925	$ 11,058
Interest cost	1,678	1,790	4,963	5,370	7,132
Expected return on plan assets	(5,379)	(4,855)	(16,079)	(14,565)	(19,922)
Amortization of prior service cost	12	15	37	45	58
Amortization of actuarial gain (loss)	627	326	1,692	975	1,384
Total net periodic benefit cost	(744)	251	(944)	750	(290)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Net period benefit cost for the pension and postretirement plans
Interest cost	35	39	105	116	150
Amortization of actuarial gain (loss)	0	(9)	0	(26)	(35)
Total net periodic benefit cost	$ 35	$ 30	$ 105	$ 90	$ 115