
6.	STOCK-BASED COMPENSATION

At December 31, 2015, we had stock-based awards outstanding under stock incentive compensation plans approved by our stockholders. Under these plans, a total of 20.6 million shares have been authorized for issuance to our directors, officers and certain other associates in the form of options, unvested restricted stock units, performance shares or other awards that are based on the value of our common stock. Shares available for future grants at December 31, 2015 were 3.8 million. The current stock plan will expire in April 2022.

STOCK OPTIONS Under the terms of the plans, stock options were granted at the market price of the stock on the grant date. The contractual term of outstanding stock options is 10 years. We issue new shares to satisfy stock-based awards.

Stock option awards became exercisable in three approximately equal annual installments beginning one year from the initial date of grant.

The following table summarizes activity relating to our stock options:



			Weighted-
	Number of		Average Exercise
	Shares		Price Per Share
	(in millions, except per share data)
Outstanding at January 1, 2013	3.0		$	27.08
Options granted	—		—
Options exercised	(0.1	)	10.59
Options canceled	(0.9	)	24.28
Outstanding at December 31, 2013	2.0		$	29.22
Options granted	—		—
Options exercised	(0.1	)	13.87
Options canceled	(1.0	)	37.70
Outstanding at December 31, 2014	0.9		$	20.66
Options granted	—		—
Options exercised	(0.1	)	17.13
Options canceled	(0.2	)	26.65
Outstanding at December 31, 2015	0.6		$	18.58

Exercisable at December 31, 2013	2.0		$	29.22
Exercisable at December 31, 2014	0.9		$	20.66
Exercisable at December 31, 2015	0.6		$	18.58

As of December 31, 2015, there were no unvested stock options. The total intrinsic value of options outstanding and exercisable as of December 31, 2015 was $2.0 million. The total intrinsic value of stock options exercised was $0.3 million in 2015, $0.5 million in 2014 and $0.8 million in 2013.

The following is a summary of the range of exercise prices for stock options that are outstanding and exercisable at December 31, 2015:



	Stock Options	Weighted-		Weighted-
Range of	Outstanding and	Average Exercise		Average
Exercise Prices	Exercisable	Price Per Share		Contractual Life
	(in millions, except per share data)			(in years)
$9.19 - $10.08	0.2	$	9.43	2.6
$15.58 - $26.02	0.4	21.47		0.8
	0.6	$	18.58	1.2

RESTRICTED STOCK UNITS We have awarded restricted stock units (RSUs). Compensation expense associated with RSUs settled in stock is recorded to paid-in-capital ratably over the three-year vesting period.

The following table summarizes activity relating to our RSUs:



			Weighted-Average
	Number of		Grant Date Fair
	Shares/Units		Value per Share/Unit
	(in millions, except per share data)
Outstanding at January 1, 2013	1.1		$	11.08
Granted	0.9		12.79
Vested	(0.7	)	11.06
Canceled	—		—
Outstanding at December 31, 2013	1.3		$	12.24
Granted	0.5		19.58
Vested	(0.1	)	13.95
Canceled	(0.1	)	12.76
Outstanding at December 31, 2014	1.6		$	14.54
Granted	0.5		25.21
Vested	(0.3	)	11.03
Canceled	(0.1	)	19.99
Outstanding at December 31, 2015	1.7		$	18.19

As of December 31, 2015, unrecognized compensation cost related to unvested RSUs totaled $10.9 million. The weighted average period over which this cost is expected to be recognized is approximately one year. In 2015 and 2014, the total fair market value of RSUs vested was $9.5 million and $1.7 million, respectively.

PERFORMANCE SHARES As of December 31, 2015, we have performance shares (PS) outstanding under our 2012 Omnibus Incentive Plan. We grant performance shares payable in stock to officers which vest in full over a three-year performance period. These grants are based equally on a total shareholder return (TSR) measure and AAM's three-year earnings before interest, taxes, depreciation and amortization (EBITDA) margin. The TSR metric compares our TSR over the three-year performance period relative to the TSR of our pre-defined competitor peer group. Share price appreciation and dividends paid are measured over the performance period to determine TSR. As these awards are settled in stock, the compensation expense booked ratably over the vesting period is recorded to paid-in-capital.

The following table summarizes activity relating to our performance shares:



		Weighted Average
	Number of	Grant Date Fair
	Shares	Value per Share
EBITDA Awards	(in millions, except per share data)
Outstanding at January 1, 2014	—	$	—
Granted	0.2	27.66
Vested	—	—
Canceled	—	—
Outstanding at December 31, 2014	0.2	$	27.66
Granted	0.1	37.68
Vested	—	—
Canceled	—	—
Outstanding at December 31, 2015	0.3	$	32.27

TSR Awards
Outstanding at January 1, 2014	—	$	—
Granted	0.2	21.11
Vested	—	—
Canceled	—	—
Outstanding at December 31, 2014	0.2	$	21.11
Granted	0.1	31.22
Vested	—	—
Canceled	—	—
Outstanding at December 31, 2015	0.3	$	25.77

We estimate the fair value of our EBITDA performance shares on the date of grant using our estimated three-year EBITDA margin, based on AAM's budget and long-range plan assumptions at that time, and adjust quarterly as necessary. We estimated the fair value of our TSR performance shares on the date of grant using the Monte Carlo simulation approach. The Monte Carlo simulation approach utilizes inputs on volatility assumptions, risk free rates, the price of the Company’s and our competitor peer group's common stock and their correlation as of each valuation date. Volatility assumptions are based on historical and implied volatility measurements.

Based on the current fair value, the estimated unrecognized compensation cost related to unvested PS totaled $9.4 million, as of December 31, 2015. The weighted-average period over which this cost is expected to be recognized is approximately one year.

PERFORMANCE AWARDS As of December 31, 2015, we have no TSR performance awards outstanding. We granted performance awards payable in cash to our officers and executives which vested in full over a three year performance period. The payout of these awards was based on a TSR measure that compared our TSR over the three-year performance period relative to the TSR of our pre-defined competitor peer group. Share price appreciation and dividends paid were measured over the performance period to determine TSR.

According to the applicable accounting guidance, these awards were considered to be stock-based compensation because the final payout amount was based “at least in part” on the price of our shares. However, as these awards were settled in cash, they are determined to be liability awards and have been remeasured at the end of each reporting period until settlement. The fair value of the performance awards was calculated on a quarterly basis using the Monte Carlo simulation approach, described above, and the liability was adjusted accordingly based on changes to the fair value and the percentage of time vested.

We recognized compensation expense associated with these performance awards of approximately $1.4 million in 2014 and $7.9 million in 2013. We made a cash payment of $3.7 million and $8.5 million in 2015 and 2014, respectively, related to the TSR performance awards.