Consolidated Statement of Changes in Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retained Earnings [Member]
Common stock per share dividend amount	$ 3.55	$ 3.00	$ 2.80
Series A Warrants [Member]
Exercise of warrants into shares of common stock	136,676	204,133
Series A Warrants [Member] \| Treasury Stock [Member]
Exercise of warrants into shares of common stock	257,630	374,786	87,381
Exercise of warrants into shares of common stock	136,676	204,133	41,439

Number of shares issued during the period as a result of the conversion of convertible securities.

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration