CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Common stock, par value beginning balance	$ 0.001	$ 0.001	$ 0.001
Options exercised, shares	142,203	85,532	435,665
Conversion of common stock units, shares	15,629	8,293	10,834
Conversion of restricted stock units, shares	222,297	198,681	169,444
Cash dividends, per share	$ 1.06	$ 1.00	$ 0.92
Treasury stock, beginning balance, shares	23,971,522	23,308,430	23,117,554
Treasury stock, acquisition of shares	701,410	663,092	190,876
Treasury stock, ending balance, shares	24,672,932	23,971,522	23,308,430