CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Treasury Stock - Common [Member]
Purchase of shares for company benefit plans (in shares)	1,451,478	1,185,517
Release of shares from company benefit plans (in shares)	275,407	38,013
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