Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2019

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, 2019	48,910	$	71.14	383,797		$	85.59	125,809	$	82.55	2,352,008		$	63.55
Authorized	—	—		—		—		—	—		—		—
Granted	—	—		1,631		91.95		—	—		—		—
Exercised/vested	—	—		(17,800	)	65.11		—	—		(83,065	)	58.82
Forfeited/expired	—	—		(998	)	92.65		—	—		(4,500	)	65.11
Balance, March 31, 2019	48,910	$	71.14	366,630		$	86.59	125,809	$	82.55	2,264,443		$	63.72

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   March 31,
	2019		2018
New shares issued from available authorized shares	—		—
Issued from available treasury stock	100,865		318,110
Total	100,865		318,110
Proceeds from stock option exercises	$	4,885	$	19,165

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   March 31,
	2019		2018
Stock options	$	382	$	1,085
Non-vested stock awards/stock units	2,135		1,468
Director deferred stock units	—		—
Performance stock units	1,137		622
Total	$	3,654	$	3,175
Income tax benefit	$	584	$	667

Unrecognized Stock-Based Compensation Expense

Unrecognized stock-based compensation expense at March 31, 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	$	866
Non-vested stock awards/stock units	15,724
Performance stock units	5,390
Total	$	21,980