Consolidated Statements of Comprehensive Income (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net loss arising during the period, tax benefit	$ (1,826)	$ (1,913)	$ (15,598)
Amortization of actuarial loss included in net periodic cost, tax expense	7,042	7,794	6,488
Amortization of prior service credit included in net periodic cost, tax benefit	(3,260)	(3,396)	(3,468)
Cash flow hedge, tax effect	$ 448	$ 0	$ 0