CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - shares	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Treasury Stock - Common [Member]
Purchase of shares for company benefit plans (in shares)	1,468,524	1,189,813
Release of shares from company benefit plans (in shares)	389,857	73,990
Preferred Stock, Exchanged for Shares of Common Stock [Member] | Preferred stock [Member]
Conversion of stock, shares converted (in shares)	0	236,048
Preferred Stock, Exchanged for Shares of Common Stock [Member] | Additional Paid-in Capital [Member]
Exchange of preferred stock (in shares)	0	9,965,835