Stock-based Compensation

Stock Compensation Plans

Pursuant to stockholder approved plans, the Company has and is permitted to grant stock-based awards to certain employees, consultants or non-employee directors of the Company and its subsidiaries or affiliates. As of December 31, 2015, the Company has 12.3 million shares available for future issuance pursuant to its 2013 Long-Term Incentive Plan ("LTI Plan"). Of these shares remaining available for future issuance, approximately 1.8 million may be issued pursuant to outstanding RSUs granted under the LTI Plan.

Restricted Stock Awards and Restricted Stock Units

During the year ended December 31, 2013, the Company issued RSAs to certain executives and employees. During the year ended December 31, 2014, in conjunction with the adoption of the LTI Plan, the Company began issuing RSUs to certain executives and employees; each RSU represents a contingent right to receive one share of common stock subject to satisfaction of the applicable vesting terms. The RSAs and RSUs granted to certain executives and employees include (1) annual performance awards that often include provisions for forfeiture by the employee if certain market performance of the Company's common stock is not achieved, (2) new hire or promotional awards that generally contain only service conditions, or (3) other awards related to specific business initiatives or compensation objectives including retention and merger integration. Generally, such awards vest over periods of approximately three years.

The following is a summary of the RSA and RSU activity during the year ended December 31, 2015.



	RSAs		RSUs
	(In thousands)		(In thousands)
Outstanding at the beginning of year	1,440		950
Granted	—		1,027
Vested	(770	)	(176	)
Forfeited	(7	)	(24	)
Outstanding at end of year	663		1,777

The Company granted approximately 1.0 million RSUs to the Company's executives and certain other employees for each of the years ended December 31, 2015 and 2014. The Company granted approximately 1.0 million shares of RSAs to the Company's executives and certain other employees for the year ended December 31, 2013. The weighted-average grant-date fair value per share of the grants for the years ended December 31, 2015, 2014, and 2013 was $69.96, $57.78, and $46.37 per share, respectively. The weighted-average requisite service period for the RSUs granted during 2015 was approximately 2.5 years.

The approximately 1.0 million RSUs granted during the year ended December 31, 2015, were comprised of (1) approximately 0.5 million RSUs that time vest over a three-year period, and (2) approximately 0.5 million RSUs to the Company's executives and certain other employees which may vest on the third anniversary of the grant date based upon the Company's total shareholder returns (defined as share price appreciation plus the value of dividends paid during the performance period) compared to that of selected peer companies. Certain RSA and RSU agreements contain provisions that result in forfeiture by the employee of any unvested shares in the event that the Company's common stock does not achieve certain price targets. To the extent that the requisite service is rendered, compensation cost for accounting purposes is not reversed; rather, it is recognized regardless of whether or not the market performance target is achieved.

The following table summarizes the assumptions used in the Monte Carlo simulation to determine the grant-date fair value for the awards granted during the years ended December 31, 2015, 2014, and 2013, respectively, with market conditions.



	Years Ended December 31,
	2015		2014		2013
Risk-free rate	1.0	%	0.7	%	0.4	%
Expected volatility	19	%	22	%	23	%
Expected dividend rate	4.21	%	1.93	%	—	%

The Company recognized aggregate stock-based compensation expense related to RSAs and RSUs of $57.1 million, $45.8 million, and $37.8 million for the years ended December 31, 2015, 2014, and 2013, respectively. The aggregate unrecognized compensation (net of estimated forfeitures) related to RSAs and RSUs at December 31, 2015 is $51.5 million and is estimated to be recognized over a weighted-average period of less than one year.

The following table is a summary of the awards vested during the three years ended December 31, 2015.



Years Ended December 31,	Total Shares Vested	Fair Value on Vesting Date
	(In thousands of shares)
2015	946	$	83,244
2014	842	62,686
2013	978	66,666

Stock-based Compensation

The following table discloses the components of stock-based compensation expense.



	Years Ended December 31,
	2015		2014		2013
Stock-based compensation expense:
Site rental costs of operations	$	8,969	$	6,565	$	1,193
Network services and other costs of operations	5,370		4,889		1,799
General and administrative expenses	52,809		44,977		36,038
Total stock-based compensation	$	67,148	$	56,431	$	39,030