Consolidated Statements of Shareholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Consolidated Statements of Shareholders' Equity and Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Available-for-sale Securities, Tax	$ (4,903)	$ (3,629)	$ 9,951
Change in pension funding status, tax effect	$ (752)	$ 4,774	$ (18,432)
Cash dividends declared (in dollars per share)	$ 0.45	$ 0.35	$ 0.25