Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Share-based Compensation [Abstract]

Target grants performance share

Target grants of performance shares outstanding at December 31, 2017, were as follows:

Grant Date	Performance Period	Target Grant of Shares
February 2016	2016-2018	258,825
March 2016	2016-2018	2,151
February 2017	2017-2019	164,558

Schedule of share-based payment award, performance shares, valuation assumptions

Assumptions used for grants of performance shares issued in 2017, 2016 and 2015 were:

				2017						2016						2015
Weighted average grant-date fair value					$24.31						$14.60						$18.98
Blended volatility range	22.70	%	–	25.56		%	29.25	%	–	32.51		%	22.86	%	–	24.61		%
Risk-free interest rate range	.69	%	–	1.61		%	.47	%	–	.92		%	.05	%	–	1.07		%
Weighted average discounted dividends per share					$1.70						$1.56						$1.57

Summary of the status of the performance share awards

A summary of the status of the performance share awards for the year ended December 31, 2017, was as follows:

	Number of Shares	Weighted Average Grant-Date Fair Value
Nonvested at beginning of period	664,188	$	21.47
Granted	203,646	24.31
Additional performance shares earned	81,643	19.22
Less:
Vested	360,319	24.88
Forfeited	163,624	24.46
Nonvested at end of period	425,534	$	18.35