Stock-Based Compensation

The Company’s incentive compensation plans allow the Company to grant awards to employees in the form of stock options, stock awards, restricted stock units, stock appreciation rights, performance stock units, dividend equivalents and other awards. Compensation related to these awards is determined based on the grant-date fair value and is amortized to expense over the vesting period. The Company recognizes compensation expense based on the earlier of the vesting date or the date when the employee becomes eligible to retire without forfeiture of the award. If awards can be settled in cash, these awards are recorded as liabilities and marked to market.

The following table discloses the amount of stock-based compensation expense:



	Three Months Ended June 30,				Six Months Ended June 30,
	2017		2016		2017		2016
Stock options	$	—	$	27	$	14	$	458
Restricted stock units	1,082		1,946		1,782		3,769
Performance stock units	210		2,974		779		5,472
Total stock-based compensation	$	1,292	$	4,947	$	2,575	$	9,699

Stock Options

No stock options were granted in the six month periods ended June 30, 2017 and 2016, respectively. In February 2014, employees participating in the 2014-2016 Long-Term Incentive Plan were granted 380,064 stock options which vested one-third each year through February 2017. In February 2013, employees participating in the 2013-2015 Long-Term Incentive Plan were granted 330,639 stock options which vested one-third each year through February 2016.

The following table provides details of the stock option activity for the six months ended June 30, 2017:



	Number of Shares
Outstanding at December 31, 2016	495,704
Exercised	(204,384	)
Expired	—
Canceled	—
Outstanding at June 30, 2017	291,320
Exercisable	291,320

Restricted Stock Units

Under the Company's Incentive Compensation Plans, restricted stock units may be granted to officers and certain other employees as awards for exceptional performance, as a hiring or retention incentive or as part of the Long-Term Incentive Plan. In February 2017, employees participating in the 2017-2019 Long-Term Incentive Plan were granted 82,563 restricted stock units which vest one-third each year through February 2020. In February 2016, employees participating in the 2016-2018 Long-Term Incentive Plan were granted 106,287 restricted stock units which vest one-third each year through February 2019. In February 2015, employees participating in the 2015-2017 Long-Term Incentive Plan were granted 105,102 restricted stock units which vest one-third each year through February 2018. Compensation related to the restricted stock units granted is determined based on the fair value of the Company’s stock on the date of grant. The Company recognizes compensation expense based on the earlier of the vesting date or the date when the employee becomes eligible to retire. Employees must remain employed for at least six months to vest in the restricted stock units, even if retirement eligible. The weighted average fair values of restricted stock units granted in the first half of 2017 and for the full year 2016 were $38.73 and $36.02, respectively.

The following table provides details of the nonvested restricted stock unit activity for the six months ended June 30, 2017:



	Number of Restricted Stock Units
Nonvested at December 31, 2016	240,574
Granted	94,707
Vested	(117,198	)
Canceled	(7,829	)
Accrued dividend equivalents	1,293
Nonvested at June 30, 2017	211,547

Performance Stock Units

Employees participating in the Company’s Long-Term Incentive Plan earn performance stock units. Under the Company’s 2017 – 2019 Long-Term Incentive Plan, any units earned during 2017 will vest at December 31, 2019. Under the Company’s 2016 – 2018 Long-Term Incentive Plan, any units earned during 2016 and 2017 will vest at December 31, 2018. Under the Company’s 2015 – 2017 Long-Term Incentive Plan, any units earned during 2015, 2016 and 2017 will vest at December 31, 2017.

The following table provides details of the nonvested performance stock units under the Company’s Long-Term Incentive Plan:



	Number of Performance Stock Units
Performance stock units outstanding at December 31, 2016	163,967
Granted	64,208
Canceled	(6,807	)
Accrued dividend equivalents	942
Performance stock units outstanding at June 30, 2017	222,310

The Company’s restricted stock units and performance stock units are not participating securities. These units will be converted into shares of Company common stock in accordance with the distribution date indicated in the agreements. Restricted stock units earn dividend equivalents from the time of the grant until distribution is made in common shares. Performance stock units earn dividend equivalents from the time the units have been notionally earned based upon Company performance metrics, until distribution is made in common shares. Dividend equivalents are only earned subject to vesting of the underlying restricted stock units and performance stock units. Accordingly, such units do not represent participating securities.