Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 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	—	—		—		—		—	—		—		—
Exercised/vested	—	—		—		—		—	—		(318,110	)	60.25
Forfeited/expired	—	—		(3,527	)	86.54		—	—		(29,125	)	69.67
Balance, March 31, 2018	53,008	$	64.87	309,129		$	81.66	80,103	$	79.91	2,569,907		$	63.65

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,
	2018		2017
New shares issued from available authorized shares	—		283,342
Issued from available treasury stock	318,110		158,712
Total	318,110		442,054
Proceeds from stock option exercises	$	19,165	$	24,747

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,
	2018		2017
Stock options	$	1,085	$	1,787
Non-vested stock awards/stock units	1,468		1,033
Director deferred stock units	—		—
Performance stock units	622		283
Total	$	3,175	$	3,103
Income tax benefit	$	667	$	1,086

Unrecognized Stock-Based Compensation Expense

Unrecognized stock-based compensation expense at March 31, 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	$	4,148
Non-vested stock awards/stock units	13,218
Performance stock units	4,507
Total	$	21,873