Postretirement Benefits (Details 8) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Amounts recognized in other comprehensive income for pension plans:
Net actuarial (gain) loss arising during the year	$ (23,810)	$ 98,303
Amortization of net actuarial loss	(14,031)	(6,344)
Amortization of prior service cost	(670)	(712)
Amendments	0	164
Total recognized in other comprehensive income	$ (38,511)	$ 91,411
Number of new plan participants resulting in charges recognized as amendments		4