Benefit Plans - Pre Tax Components of Accumulated Other Comprehensive Loss Related to Pension Plans and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits
Benefit Plans
Net actuarial loss (gain)	$ 99,078	$ 108,137
Prior service cost	4,760	4,950
Total accumulated other comprehensive loss (income)	103,838	113,087
Other Postretirement Benefits
Benefit Plans
Net actuarial loss (gain)	(5,408)	771
Prior service cost	0	0
Total accumulated other comprehensive loss (income)	$ (5,408)	$ 771