Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2018

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

Summary of Activity in Corporation's Active Stock Plans

	Director Deferred Stock Units Outstanding				Non-Vested Stock Awards/Stock Units Outstanding				Performance Stock Units Outstanding			Stock Options Outstanding
	Number of Units		Weighted- Average Fair Value at Grant		Number of Shares/Units		Weighted- Average Fair Value at Grant		Number of Units	Weighted- Average Fair Value at Grant		Number of Shares		Weighted- Average Exercise Price
Balance, January 1, 2018	53,008		$	64.87	312,656		$	81.71	80,103	$	79.91	2,917,142		$	63.34
Authorized	—		—		—		—		—	—		—		—
Granted	6,576		109.58		—		—		—	—		—		—
Exercised/vested	(10,674	)	63.68		(2,470	)	78.92		—	—		(434,687	)	61.12
Forfeited/expired	—		—		(4,836	)	87.00		—	—		(49,125	)	70.70
Balance, September 30, 2018	48,910		$	71.14	305,350		$	81.65	80,103	$	79.91	2,433,330		$	63.59

Shares Issued in Connection with Stock Compensation Awards

Shares issued in connection with stock compensation awards along with other related information were as follows:

	Three Months Ended   September 30,				Nine Months Ended   September 30,
	2018		2017		2018		2017
New shares issued from available authorized shares	—		9,299		—		602,662
Issued from available treasury stock	19,232		13,425		447,831		172,137
Total	19,232		22,724		447,831		774,799
Proceeds from stock option exercises	$	1,119	$	1,274	$	26,567	$	45,422

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]

Stock-based compensation expense and the related income tax benefit is presented in the following table.

	Three Months Ended   September 30,				Nine Months Ended   September 30,
	2018		2017		2018		2017
Stock options	$	960	$	1,532	$	3,064	$	4,892
Non-vested stock awards/stock units	1,357		813		4,196		2,747
Director deferred stock units	—		—		720		519
Performance stock units	479		377		1,576		855
Total	$	2,796	$	2,722	$	9,556	$	9,013
Income tax benefit	$	587	$	953	$	2,007	$	3,155

Unrecognized Stock-Based Compensation Expense

Unrecognized stock-based compensation expense at September 30, 2018 is presented in the table below. Unrecognized stock-based compensation expense related to performance stock units is presented assuming attainment of the maximum payout rate as set forth by the performance criteria.

Stock options	$	1,906
Non-vested stock awards/stock units	10,343
Performance stock units	3,553
Total	$	15,802