Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

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

Summary of Activity in Corporation's Active Stock Plans

A combined summary of activity in our active stock plans is presented in the table. Performance stock units outstanding are presented assuming attainment of the maximum payout rate as set forth by the performance criteria. As of June 30, 2019, there were 1,265,480 shares remaining available for grant for future stock-based compensation awards.

	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, 2019	48,910	$	71.14	383,797		$	85.59	125,809	$	82.55	2,352,008		$	63.55
Authorized	—	—		—		—		—	—		—		—
Granted	7,592	102.70		1,957		91.96		—	—		—		—
Exercised/vested	—	—		(17,800	)	65.11		—	—		(136,100	)	57.61
Forfeited/expired	—	—		(3,877	)	90.10		—	—		(6,875	)	65.11
Balance, June 30, 2019	56,502	$	75.38	364,077		$	86.58	125,809	$	82.55	2,209,033		$	63.91

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   June 30,				Six Months Ended   June 30,
	2019		2018		2019		2018
New shares issued from available authorized shares	—		—		—		—
Issued from available treasury stock	53,035		110,489		153,900		428,599
Total	53,035		110,489		153,900		428,599
Proceeds from stock option exercises	$	2,956	$	6,283	$	7,841	$	25,448

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   June 30,				Six Months Ended   June 30,
	2019		2018		2019		2018
Stock options	$	379	$	1,019	$	761	$	2,104
Non-vested stock awards/stock units	2,056		1,371		4,191		2,839
Director deferred stock units	780		720		780		720
Performance stock units	1,149		475		2,286		1,097
Total	$	4,364	$	3,585	$	8,018	$	6,760
Income tax benefit	$	732	$	753	$	1,316	$	1,420

Unrecognized Stock-Based Compensation Expense

Unrecognized stock-based compensation expense at June 30, 2019 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	$	465
Non-vested stock awards/stock units	13,441
Performance stock units	4,241
Total	$	18,147