Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Restricted and Deferred Stock Activity

A summary of restricted and deferred stock activity follows:

	Number of shares
Non-vested shares outstanding at January 1, 2017	1,321,292
Awarded:
Time-vesting	144,141
Performance-based	149,843
Released:
Time-vesting	(351,403	)
Performance-based	(115,732	)
Forfeitures:
Time-vesting	(35,550	)
Performance-based	(58,749	)
Non-vested shares outstanding at December 31, 2017	1,053,842

Summary of Average Grant-Date Fair Value of Restricted Stock

he average grant-date fair value of restricted stock awarded in 2017, 2016 and 2015 follows:

	2017		2016		2015
Time-vested	$	55.55	$	51.04	$	53.65
Performance-based	51.90		51.18		49.50

Schedule of Weighted Average Assumptions on Performance-Based Shares

The fair values of the performance-based awards that include a market condition were calculated using a Monte Carlo valuation model and the following weighted average assumptions:

	2017		2016		2015
Risk-free interest rate	1.4	%	1.2	%	1.1	%
Expected term (years)	3		3		3
Expected stock price volatility	21.1	%	19.8	%	17.4	%