CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
CONSOLIDATED BALANCE SHEETS
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Common stock, par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	80,266,365	79,781,305
Treasury stock, at cost, shares	28,423,779	28,015,386