CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - Treasury Stock [Member] - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Purchase of treasury stock (in shares)	0	35,000	3,316,000
Treasury stock issued upon exercise of stock options and issuance of restricted stock (in shares)	138,000	170,000	166,000