Postretirement Benefits (Details 7) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Amounts included in accumulated other comprehensive income
Net actuarial loss	$ 148,865	$ 186,707
Prior service cost	4,605	5,274
Net amount not yet recognized	153,470	$ 191,981
Amounts that will be amortized from accumulated other comprehensive income into pension cost during next fiscal year
Estimated net actuarial loss that will be amortized from accumulated other comprehensive income into pension cost during next fiscal year, before tax	7,600
Estimated net prior service cost that will be amortized from accumulated other comprehensive income into pension cost during next fiscal year, before tax	$ 700