Stock Plans (Tables)

9 Months Ended

Sep. 30, 2017

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

Schedule of Stock Compensation Expense

Stock compensation expense is as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
(In thousands)	2017		2016		2017		2016
Stock compensation expense	$	1,435	$	1,341	$	9,668	$	8,292
Income tax benefit	543		515		3,650		3,210
Stock compensation expense, net of income tax benefit	$	892	$	826	$	6,018	$	5,082

Summary of Stock Option Activity

A summary of stock option activity for the nine months ended September 30, 2017 follows:

	Shares		Weighted Average Exercise Price
Outstanding at January 1, 2017	1,576,092		$	37.63
Exercised	(422,711	)	29.32
Outstanding at September 30, 2017	1,153,381		40.68
Exercisable at September 30, 2017	785,377		$	38.11

Summary of Restricted Stock and Unit Activity

A summary of restricted stock and unit activity for the nine months ended September 30, 2017 follows:

	Shares		Weighted Average Grant Date Fair Value
Unvested at January 1, 2017	234,592		$	49.76
Granted	65,683		74.90
Vested	(72,128	)	51.35
Forfeited	(3,174	)	50.11
Unvested at September 30, 2017	224,973		$	57.16

Schedule of Fair Value Assumptions for Units

The following weighted average assumptions were used in the Monte Carlo model for units granted in the first quarter of 2017 with a market condition modifier.

Fair value per unit	$72.28
Risk-free interest rate	1.45%
Expected dividend yield	2.31%
Expected volatility	29.1%
MSA stock beta	1.272

Summary of Performance Stock Unit Activity

A summary of performance stock unit activity for the nine months ended September 30, 2017 follows:

	Shares		Weighted Average Grant Date Fair Value
Unvested at January 1, 2017	186,621		$	46.18
Granted	98,886		72.73
Performance adjustments	27,915		57.26
Vested	(71,403	)	56.47
Unvested at September 30, 2017	242,019		$	55.06