Stock Plans (Tables)

6 Months Ended

Jun. 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 June 30,				Six Months Ended June 30,
(In thousands)	2017		2016		2017		2016
Stock compensation expense	$	1,908	$	1,453	$	8,233	$	6,951
Income tax benefit	721		563		3,107		2,695
Stock compensation expense, net of income tax benefit	$	1,187	$	890	$	5,126	$	4,256

Summary of Stock Option Activity

A summary of stock option activity for the six months ended June 30, 2017 follows:

	Shares		Weighted Average Exercise Price
Outstanding at January 1, 2017	1,576,092		$	37.63
Exercised	(412,967	)	29.20
Outstanding at June 30, 2017	1,163,125		40.63
Exercisable at June 30, 2017	795,121		$	38.07

Summary of Restricted Stock and Unit Activity

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

	Shares		Weighted Average Grant Date Fair Value
Unvested at January 1, 2017	234,592		$	49.76
Granted	49,189		73.92
Vested	(71,628	)	51.32
Forfeited	(3,174	)	50.11
Unvested at June 30, 2017	208,979		$	55.53

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 six months ended June 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	(70,403	)	57.27
Unvested at June 30, 2017	243,019		$	55.04