Stock-Based Compensation

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 March 31, 2018, there were 1,400,402 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, 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 are issued from available treasury shares. If no treasury shares are available, new shares are issued from available authorized shares. 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

Stock-based compensation expense is recognized ratably over the requisite service period for all awards. For most stock option awards, the service period generally matches the vesting period. For stock options granted to certain executive officers and for non-vested stock units granted to all participants, the service period does not extend past the date the participant reaches 65 years of age. Deferred stock units granted to non-employee directors generally have immediate vesting and the related expense is fully recognized on the date of grant. For performance stock units, the service period generally matches the three-year performance period specified by the award, however, the service period does not extend past the date the participant reaches 65 years of age. Expense recognized each period is dependent upon our estimate of the number of shares that will ultimately be issued.

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 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