Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Assumptions for Options Granted

A summary of assumptions for options granted in each of the three years 2015 through 2017 is as follows:

	2017		2016		2015
Volatility factor	14.8	%	19.2	%	23.6	%
Dividend yield	0.7	%	1.1	%	0.9	%
Expected term (in years)	5.71		5.78		5.66
Risk-free rate	2.0	%	1.3	%	1.6	%