Stock Based Compensation

The Company accounts for stock-based compensation pursuant to relevant authoritative guidance, which requires measurement of compensation cost for all stock awards at fair value on the date of grant and recognition of compensation, net of estimated forfeitures, over the requisite service period for awards expected to vest. The Company has Stock Incentive Plans (the Plans) pursuant to which the Company’s board of directors may grant stock options or restricted stock to employees. The Company is authorized to issue grants of restricted stock and stock options to purchase up to 26,963,150 shares for the years ended December 31, 2016, 2015 and 2014, respectively. On May 13, 2013, the Company’s stockholders authorized an increase of 6,500,000 shares of common stock available for grant pursuant to the 2010 Equity Compensation Plan. Giving effect to this increase, there were 2,968,584 additional shares remaining available for grant under the Plans at December 31, 2016.

The table below summarizes the expense recognized related to share-based payments recognized for the years ended December 31 (in thousands):



	2016		2015		2014
Stock options	$	35,234	$	44,260	$	13,267
Restricted stock	28,712		45,862		24,382
Stock-based compensation	$	63,946	$	90,122	$	37,649

The tax benefits recorded on stock based compensation were $35.0 million, $35.7 million and $13.0 million for the years ended December 31, 2016, 2015 and 2014, respectively.

The following table summarizes the Company’s total unrecognized compensation cost related to stock-based compensation as of December 31, 2016 (cost in thousands):

Stock Options

The following summarizes the changes in the number of shares of common stock under option for the following periods (shares and aggregate intrinsic value in thousands):



	Shares		Weighted Average Exercise Price		Options Exercisable at End of Year	Weighted Average Exercise Price of Exercisable Options		Weighted Average Fair Value of Options Granted During the Year		Aggregate Intrinsic Value
Outstanding at December 31, 2013	5,331		$	25.68	2,589	$	16.57			$	487,673
Granted	1,544		135.16					$	42.77
Exercised	(1,429	)	20.75							182,904
Forfeited	(315	)	41.72
Outstanding at December 31, 2014	5,131		58.71		2,370	21.75				461,770
Granted	654		154.56					$	35.32
Exercised	(586	)	33.97							63,863
Forfeited	(196	)	95.16
Outstanding at December 31, 2015	5,003		72.72		2,545	26.82				351,277
Granted	1,780		133.33					$	28.61
Exercised	(500	)	42.36							49,592
Forfeited	(137	)	140.67
Outstanding at December 31, 2016	6,146		$	91.20	3,429	$	55.00			$	309,238
Expected to vest at December 31, 2016	6,146		$	91.20

The following table summarizes information about stock options outstanding at December 31, 2016 (shares in thousands):



Exercise Price	Options Outstanding	Weighted Average Remaining Vesting Life in Years	Options Exercisable
$10.00 – 58.02	2,536	0.00	2,527
74.99 – 111.09	159	0.77	71
114.90 – 138.47	1,382	1.28	113
144.59 – 149.68	935	1.15	653
151.16 – 158.24	772	2.44	65
172.68 – 174.35	362	3.82	—
	6,146		3,429

The aggregate intrinsic value of stock options exercisable at December 31, 2016 was $296.7 million. The weighted average remaining contractual term of options exercisable at December 31, 2016 was 5.0 years.

The fair value of stock option awards granted was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions for grants or modifications during the years ended December 31 as follows:



	2016		2015		2014
Risk-free interest rate	1.08	%	1.47	%	1.24	%
Dividend yield	—		—		—
Expected volatility	27.29	%	27.77	%	34.61	%
Expected life (in years)	3.47		4.46		3.90

The weighted-average remaining contractual life for options outstanding was 6.7 years at December 31, 2016.

Restricted Stock

There were no restricted stock shares granted with performance based conditions or market conditions in 2016, 2015 and 2014. The following table summarizes the changes in the number of shares of restricted stock and restricted stock units for the following periods (shares in thousands):



	Shares		Weighted Average Grant Date Fair Value
Outstanding at December 31, 2013	634		$	67.83
Granted	467		146.12
Cancelled	(76	)	31.48
Issued	(309	)	74.56
Outstanding at December 31, 2014	716		121.38
Granted	126		151.33
Cancelled	(52	)	135.92
Issued	(293	)	85.40
Outstanding at December 31, 2015	497		149.40
Granted	152		128.90
Cancelled	(41	)	145.25
Issued	(229	)	151.72
Outstanding at December 31, 2016	379		$	140.39

Unrecognized
Compensation
Cost

Weighted Average
Period of Expense
Recognition
(in Years)

Stock options

Restricted stock