Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net unrealized gain (loss) on cash flow hedges, tax	$ 1,513	$ 484	$ 1,080
Net unrealized loss on investment securities, tax	(244)	(1,427)	2,775
Adjustments to pension and postretirement plans, tax	(14,430)	13,844	106,336
Amortization of pension and postretirement costs, tax	$ 17,550	$ 15,966	$ 15,643