Stock-Based Compensation

Under the Company's 2014 Stock Incentive Plan ("2014 Plan"), the Company granted restricted common stock awards and stock units ("restricted stock") and performance share units as long-term incentive award grants to employees and non-employee directors. Restricted stock granted to employees primarily vests 50% after two years and the remainder after three years from the date of grant. Restricted stock granted to non-employee directors generally vests on the first anniversary date of the grant. Under the 2014 Plan, 8 million shares are authorized for grant, of which approximately 4.4 million shares are available for future issuance as of March 31, 2018.

Restricted stock The value of restricted stock is determined by the market value of the Company’s common stock at the date of grant. In the first three months of 2018, restricted stock in the amount of 625,416 shares was granted to employees. The value of the awards is recognized as compensation expense ratably over the restriction periods. As of March 31, 2018, there was $50.6 million of unrecognized compensation expense that will be recognized over a weighted average period of 2.3 years.

The Company recorded restricted stock compensation expense of $6.5 million and $6.8 million for the three months ended March 31, 2018 and 2017, respectively.

A summary of the Company’s nonvested restricted stock for the three months ended March 31, 2018 is as follows:



	Shares subject to restriction (thousands)		Weighted average grant date fair value
Nonvested at December 31, 2017	1,593		$	38.86
Granted	625		$	52.64
Vested	(486	)	$	41.05
Forfeited	(7	)	$	49.48
Nonvested at March 31, 2018	1,725		$	43.26

Total Shareholder Return Performance Share Plans The 2014 Plan provides for awarding of performance shares to members of senior management at the end of successive three-year periods based on the Company's performance in terms of total shareholder return relative to a peer group of automotive companies. The Company recorded compensation expense of $1.7 million and $3.1 million for the three months ended March 31, 2018 and 2017, respectively.

Relative Revenue Growth Performance Share Plans The 2014 Plan also provides for awarding of performance shares to members of senior management based on the Company's performance in terms of revenue growth relative to the vehicle market over three-year performance periods. The compensation expense was $6.5 million and $3.2 million for the three months ended March 31, 2018 and 2017, respectively.

A summary of the status of the Company’s nonvested relative revenue growth performance shares for the three months ended March 31, 2018 is as follows:



	Number of shares (thousands)	Weighted average grant date fair value
Nonvested at December 31, 2017	355	$	39.42
Granted	175	$	52.64
Nonvested at March 31, 2018	530	$	43.79