Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net gain (loss) arising during the period, Tax	$ (1,913)	$ (15,598)	$ 21,424
Amortization of actuarial loss included in net periodic cost, tax	7,794	6,488	9,024
Amortization of prior service credit included in net periodic cost, tax	$ (3,396)	$ (3,468)	$ (3,482)