Condensed Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Tax expense recognized on the amortization of prior service cost	$ (7)	$ (5)	$ (20)	$ (18)
Tax expense recognized on the net gain (loss)	62	26	187	80
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	$ (51)	$ (18)	$ (29)	$ (19)