CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common stock, par value beginning balance	$ 0.001	$ 0.001	$ 0.001
Options exercised, shares	85,532	435,665	1,158,537
Conversion of common stock units, shares	8,293	10,834	11,851
Conversion of restricted stock units, shares	198,681	169,444	146,930
Cash dividends, per share	$ 1.00	$ 0.92	$ 0.78
Treasury stock, beginning balance, shares	23,308,430	23,117,554	22,943,925
Treasury stock, acquisition of shares	663,092	190,876	173,629
Treasury stock, ending balance, shares	23,971,522	23,308,430	23,117,554