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]
Change in estimated fair value of investment in debt securities, tax	$ 0	$ 4,685	$ (3,208)
Unrecognized actuarial loss and prior service cost, income taxes	4,355	24,746	(12,866)
Foreign currency translation adjustment, tax	0	82	947
Income tax on cash flow hedge activity	$ (72)	$ (154)	$ (166)